Using luma information for chroma prediction with separate luma-chroma framework in video coding

ABSTRACT

A method of decoding video data comprises receiving a bitstream of encoded video data, the encoded video data representing partitioned luma blocks and partitioned chroma blocks, wherein the chroma blocks are partitioned independently of the luma blocks, determining a respective coding mode corresponding to the respective partitioned luma blocks, decoding the respective partitioned luma blocks according to the determined respective coding modes, decoding a first syntax element indicating that the respective coding modes associated with the respective partitioned luma blocks are to be used for decoding a first partitioned chroma block, wherein the first partitioned chroma block is aligned with two or more partitioned luma blocks, determining a chroma coding mode for the first partitioned chroma block according to a function of the respective coding modes of the two or more partitioned luma blocks, and decoding the first partitioned chroma block in accordance with the determined chroma coding mode.

This application claims the benefit of U.S. Provisional Application No.62/311,265, filed Mar. 21, 2016, the entire content of which isincorporated by reference herein.

TECHNICAL FIELD

This disclosure relates to video encoding and video decoding.

BACKGROUND

Digital video capabilities can be incorporated into a wide range ofdevices, including digital televisions, digital direct broadcastsystems, wireless broadcast systems, personal digital assistants (PDAs),laptop or desktop computers, tablet computers, e-book readers, digitalcameras, digital recording devices, digital media players, video gamingdevices, video game consoles, cellular or satellite radio telephones,so-called “smart phones,” video teleconferencing devices, videostreaming devices, and the like. Digital video devices implement videocoding techniques, such as those described in the standards defined byMPEG-2, MPEG-4, ITU-T H.263, ITU-T H.264/MPEG-4, Part 10, Advanced VideoCoding (AVC), the High Efficiency Video Coding (HEVC or H.265) standard,and extensions of such standards. The video devices may transmit,receive, encode, decode, and/or store digital video information moreefficiently by implementing such video coding techniques.

Video coding techniques include spatial (intra picture) predictionand/or temporal (inter picture) prediction to reduce or removeredundancy inherent in video sequences. For block-based video coding, avideo slice (e.g., a video frame or a portion of a video frame) may bepartitioned into video blocks, which may also be referred to astreeblocks, coding units (CUs) and/or coding nodes. Pictures may bereferred to as frames, and reference pictures may be referred to asreference frames.

Spatial or temporal prediction results in a predictive block for a blockto be coded. Residual data represents pixel differences between theoriginal block to be coded and the predictive block. For furthercompression, the residual data may be transformed from the pixel domainto a transform domain, resulting in residual transform coefficients,which then may be quantized. Entropy coding may be applied to achieveeven more compression.

SUMMARY

This disclosure describes techniques for coding video data that has beenpartitioned using an independent luma and chroma partition framework. Insome examples, this disclosure describes techniques for determining howto reuse coding information from luma blocks for chroma blocks whenthere are two or more luma blocks that correspond to the chroma block(e.g., when two or more luma blocks are co-located with a chroma block).

In other examples, this disclosure describes techniques for determiningparameters for a position dependent intra prediction comparison (PDPC)mode when blocks of video data may be partitioned into non-squareblocks. In some examples, PDPC parameters may be determined usingmultiple lookup tables, including separate tables for vertical-relatedparameters and horizontal-related parameters.

In one example of the disclosure, a method of decoding video datacomprises receiving a bitstream of encoded video data, the encoded videodata representing partitioned luma blocks and partitioned chroma blocks,wherein the chroma blocks are partitioned independently of the lumablocks, determining a respective coding mode corresponding to therespective partitioned luma blocks, decoding the respective partitionedluma blocks according to the determined respective coding modes,decoding a first syntax element indicating that the respective codingmodes associated with the respective partitioned luma blocks are to beused for decoding a first partitioned chroma block, wherein the firstpartitioned chroma block is aligned with two or more partitioned lumablocks, determining a chroma coding mode for the first partitionedchroma block according to a function of the respective coding modes ofthe two or more partitioned luma blocks, and decoding the firstpartitioned chroma block in accordance with the determined chroma codingmode.

In another example of the disclosure, an apparatus configured to decodevideo data comprises a memory configured to store a bitstream of encodedvideo data and one or more processors configured to receive thebitstream of encoded video data, the encoded video data representingpartitioned luma blocks and partitioned chroma blocks, wherein thechroma blocks are partitioned independently of the luma blocks,determine a respective coding mode corresponding to the respectivepartitioned luma blocks, decode the respective partitioned luma blocksaccording to the determined respective coding modes, decode a firstsyntax element indicating that the respective coding modes associatedwith the respective partitioned luma blocks are to be used for decodinga first partitioned chroma block, wherein the first partitioned chromablock is aligned with two or more partitioned luma blocks, determine achroma coding mode for the first partitioned chroma block according to afunction of the respective coding modes of the two or more partitionedluma blocks, and decode the first partitioned chroma block in accordancewith the determined chroma coding mode.

In another example of the disclosure, an apparatus configured to decodevideo data comprises means for receiving a bitstream of encoded videodata, the encoded video data representing partitioned luma blocks andpartitioned chroma blocks, wherein the chroma blocks are partitionedindependently of the luma blocks, means for determining a respectivecoding mode corresponding to the respective partitioned luma blocks,means for decoding the respective partitioned luma blocks according tothe determined respective coding modes, means for decoding a firstsyntax element indicating that the respective coding modes associatedwith the respective partitioned luma blocks are to be used for decodinga first partitioned chroma block, wherein the first partitioned chromablock is aligned with two or more partitioned luma blocks, means fordetermining a chroma coding mode for the first partitioned chroma blockaccording to a function of the respective coding modes of the two ormore partitioned luma blocks, and means for decoding the firstpartitioned chroma block in accordance with the determined chroma codingmode.

In another example, this disclosure describes a non-transitorycomputer-readable storage medium storing instructions that, whenexecuted, causes one or more processors configured to decoded video datato receive the bitstream of encoded video data, the encoded video datarepresenting partitioned luma blocks and partitioned chroma blocks,wherein the chroma blocks are partitioned independently of the lumablocks, determine a respective coding mode corresponding to therespective partitioned luma blocks, decode the respective partitionedluma blocks according to the determined respective coding modes, decodea first syntax element indicating that the respective coding modesassociated with the respective partitioned luma blocks are to be usedfor decoding a first partitioned chroma block, wherein the firstpartitioned chroma block is aligned with two or more partitioned lumablocks, determine a chroma coding mode for the first partitioned chromablock according to a function of the respective coding modes of the twoor more partitioned luma blocks, and decode the first partitioned chromablock in accordance with the determined chroma coding mode.

In another example of the disclosure, a method of decoding video datacomprises receiving a block of video data encoded using a positiondependent intra prediction combination (PDPC) mode, the block of videodata having a non-square shape defined by a width and a height,determining one or more PDPC parameters based on one or more of thewidth or the height of the block of video data, and decoding the blockof video data using the PDPC mode and the determined PDPC parameters.

In another example of the disclosure, an apparatus configured to decodevideo data comprises a memory configured to store a block of video dataencoded using a PDPC mode, the block of video data having a non-squareshape defined by a width and a height, and one or more processorsconfigured to receive the block of video data, determine one or morePDPC parameters based on one or more of the width or the height of theblock of video data, and decode the block of video data using the PDPCmode and the determined PDPC parameters.

In another example of the disclosure, an apparatus configured to decodevideo data comprises means for receiving a block of video data encodedusing a PDPC mode, the block of video data having a non-square shapedefined by a width and a height, means for determining one or more PDPCparameters based on one or more of the width or the height of the blockof video data, and means for decoding the block of video data using thePDPC mode and the determined PDPC parameters.

In another example, this disclosure describes a non-transitorycomputer-readable storage medium storing instructions that, whenexecuted, cause one or more processors of a device to configured todecode video data to receive a block of video data encoded using a PDPCmode, the block of video data having a non-square shape defined by awidth and a height, determine one or more PDPC parameters based on oneor more of the width or the height of the block of video data, anddecode the block of video data using the PDPC mode and the determinedPDPC parameters.

In another example of the disclosure, a method of encoding video datacomprises receiving a block of video data, the block of video datahaving a non-square shape defined by a width and a height, determiningone or more PDPC parameters based on one or more of the width or theheight of the block of video data, and encoding the block of video datausing a PDPC mode and the determined PDPC parameters.

In another example of the disclosure, an apparatus configured to encodevideo data comprises a memory configured to store a block of video data,the block of video data having a non-square shape defined by a width anda height, and one or more processors configured to receive the block ofvideo data, determine one or more PDPC parameters based on one or moreof the width or the height of the block of video data, and encode theblock of video data using a PDPC mode and the determined PDPCparameters.

The details of one or more aspects of the disclosure are set forth inthe accompanying drawings and the description below. Other features,objects, and advantages of the techniques described in this disclosurewill be apparent from the description and drawings, and from the claims.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a block diagram illustrating an example video encoding anddecoding system configured to implement techniques of the disclosure.

FIG. 2A is a conceptual diagram illustrating an example of blockpartitioning using a quadtree plus binary tree (QTBT) structure.

FIG. 2B is a conceptual diagram illustrating an example tree structurecorresponding to the block partitioning using the QTBT structure of FIG.2A.

FIG. 3 is a conceptual diagram illustrating an example of luma andchroma relative partitioning in accordance with the techniques of thisdisclosure.

FIG. 4 is a conceptual diagram illustrating another example of luma andchroma relative partitioning in accordance with the techniques of thisdisclosure.

FIG. 5A illustrates a prediction of a 4×4 block using an unfilteredreference according to techniques of this disclosure.

FIG. 5B illustrates a prediction of a 4×4 block using a filteredreference according to techniques of this disclosure.

FIG. 6 is a conceptual diagram illustrating the use of nested tables fordetermining a set of prediction parameters used in a rectangular blockin accordance with one example of the disclosure.

FIG. 7 is a block diagram illustrating an example of a video encoderconfigured to implement techniques of the disclosure.

FIG. 8 is a block diagram illustrating an example of a video decoderconfigured to implement techniques of the disclosure.

FIG. 9 is a flowchart illustrating an example operation of a video coderin accordance with a technique of this disclosure.

FIG. 10 is a flowchart illustrating an example operation of a videodecoder in accordance with a technique of this disclosure.

FIG. 11 is a flowchart illustrating an example operation of a videoencoder in accordance with a technique of this disclosure.

FIG. 12 is a flowchart illustrating an example operation of a videodecoder in accordance with a technique of this disclosure.

DETAILED DESCRIPTION

According to some video block partitioning techniques, chroma blocks ofvideo data are partitioned independently of luma blocks of video data,such that some chroma blocks may not be directly aligned with a singlecorresponding luma block. As such, it becomes difficult to reuse syntaxelements related to luma blocks for chroma blocks, as there may not be aone-to-one correspondence between luma blocks and chroma blocks. Thisdisclosure describes techniques for coding a chroma block of video datausing information (e.g., syntax elements) corresponding to a luma blockof video data in situations where luma and chroma blocks are partitionedindependently.

This disclosure also describes techniques for determining codingparameters for a position dependent intra prediction combination (PDPC)coding mode. In one example, this disclosure describes techniques fordetermining PDPC parameters for video blocks partitioned into non-squareblocks (e.g., non-square, rectangular blocks).

FIG. 1 is a block diagram illustrating an example video encoding anddecoding system 10 that may be configured to perform the techniques ofthis disclosure. As shown in FIG. 1, system 10 includes source device 12that provides encoded video data to be decoded at a later time bydestination device 14. In particular, source device 12 provides thevideo data to destination device 14 via computer-readable medium 16.Source device 12 and destination device 14 may comprise any of a widerange of devices, including desktop computers, notebook (e.g., laptop)computers, tablet computers, set-top boxes, telephone handsets such asso-called “smart” phones (or more generally, mobile stations), tabletcomputers, televisions, cameras, display devices, digital media players,video gaming consoles, video streaming device, or the like. A mobilestation may be any device capable of communicating over a wirelessnetwork. In some cases, source device 12 and destination device 14 maybe equipped for wireless communication. Thus, source device 12 anddestination device 14 may be wireless communication devices (e.g.,mobile stations). Source device 12 is an example video encoding device(i.e., a device for encoding video data). Destination device 14 is anexample video decoding device (i.e., a device for decoding video data).

In the example of FIG. 1, source device 12 includes video source 18,storage media 20 configured to store video data, video encoder 22, andoutput interface 24. Destination device 14 includes input interface 26,storage media 28 configured to store encoded video data, video decoder30, and display device 32. In other examples, source device 12 anddestination device 14 include other components or arrangements. Forexample, source device 12 may receive video data from an external videosource, such as an external camera. Likewise, destination device 14 mayinterface with an external display device, rather than including anintegrated display device 32.

The illustrated system 10 of FIG. 1 is merely one example. Techniquesfor processing and/or coding (e.g., encoding and/or decoding) video datamay be performed by any digital video encoding and/or decoding device.Although the techniques of this disclosure are generally performed by avideo encoding device and/or video decoding device, the techniques mayalso be performed by a video encoder/decoder, typically referred to as a“CODEC.” Source device 12 and destination device 14 are merely examplesof such coding devices in which source device 12 generates coded videodata for transmission to destination device 14. In some examples, sourcedevice 12 and destination device 14 may operate in a substantiallysymmetrical manner such that each of source device 12 and destinationdevice 14 include video encoding and decoding components. Hence, system10 may support one-way or two-way video transmission between sourcedevice 12 and destination device 14, e.g., for video streaming, videoplayback, video broadcasting, or video telephony.

Video source 18 of source device 12 may include a video capture device,such as a video camera, a video archive containing previously capturedvideo, and/or a video feed interface to receive video data from a videocontent provider. As a further alternative, video source 18 may generatecomputer graphics-based data as the source video, or a combination oflive video, archived video, and computer-generated video. Source device12 may comprise one or more data storage media (e.g., storage media 20)configured to store the video data. The techniques described in thisdisclosure may be applicable to video coding in general, and may beapplied to wireless and/or wired applications. In each case, thecaptured, pre-captured, or computer-generated video may be encoded byvideo encoder 22. Output interface 24 may output the encoded videoinformation (e.g., a bitstream of encoded video data) tocomputer-readable medium 16.

Destination device 14 may receive the encoded video data to be decodedvia computer-readable medium 16. Computer-readable medium 16 maycomprise any type of medium or device capable of moving the encodedvideo data from source device 12 to destination device 14. In someexamples, computer-readable medium 16 comprises a communication mediumto enable source device 12 to transmit encoded video data directly todestination device 14 in real-time. The encoded video data may bemodulated according to a communication standard, such as a wirelesscommunication protocol, and transmitted to destination device 14. Thecommunication medium may comprise any wireless or wired communicationmedium, such as a radio frequency (RF) spectrum or one or more physicaltransmission lines. The communication medium may form part of apacket-based network, such as a local area network, a wide-area network,or a global network such as the Internet. The communication medium mayinclude routers, switches, base stations, or any other equipment thatmay be useful to facilitate communication from source device 12 todestination device 14. Destination device 14 may comprise one or moredata storage media configured to store encoded video data and decodedvideo data.

In some examples, encoded data may be output from output interface 24 toa storage device. Similarly, encoded data may be accessed from thestorage device by input interface. The storage device may include any ofa variety of distributed or locally accessed data storage media such asa hard drive, Blu-ray discs, DVDs, CD-ROMs, flash memory, volatile ornon-volatile memory, or any other suitable digital storage media forstoring encoded video data. In a further example, the storage device maycorrespond to a file server or another intermediate storage device thatmay store the encoded video generated by source device 12. Destinationdevice 14 may access stored video data from the storage device viastreaming or download. The file server may be any type of server capableof storing encoded video data and transmitting that encoded video datato the destination device 14. Example file servers include a web server(e.g., for a website), an FTP server, network attached storage (NAS)devices, or a local disk drive. Destination device 14 may access theencoded video data through any standard data connection, including anInternet connection. This may include a wireless channel (e.g., a Wi-Ficonnection), a wired connection (e.g., DSL, cable modem, etc.), or acombination of both that is suitable for accessing encoded video datastored on a file server. The transmission of encoded video data from thestorage device may be a streaming transmission, a download transmission,or a combination thereof.

The techniques described in this disclosure may be applied to videocoding in support of any of a variety of multimedia applications, suchas over-the-air television broadcasts, cable television transmissions,satellite television transmissions, Internet streaming videotransmissions, such as dynamic adaptive streaming over HTTP (DASH),digital video that is encoded onto a data storage medium, decoding ofdigital video stored on a data storage medium, or other applications. Insome examples, system 10 may be configured to support one-way or two-wayvideo transmission to support applications such as video streaming,video playback, video broadcasting, and/or video telephony.

Computer-readable medium 16 may include transient media, such as awireless broadcast or wired network transmission, or storage media (thatis, non-transitory storage media), such as a hard disk, flash drive,compact disc, digital video disc, Blu-ray disc, or othercomputer-readable media. In some examples, a network server (not shown)may receive encoded video data from source device 12 and provide theencoded video data to destination device 14, e.g., via networktransmission. Similarly, a computing device of a medium productionfacility, such as a disc stamping facility, may receive encoded videodata from source device 12 and produce a disc containing the encodedvideo data. Therefore, computer-readable medium 16 may be understood toinclude one or more computer-readable media of various forms, in variousexamples.

Input interface 26 of destination device 14 receives information fromcomputer-readable medium 16. The information of computer-readable medium16 may include syntax information defined by video encoder 22 of videoencoder 22, which is also used by video decoder 30, that includes syntaxelements that describe characteristics and/or processing of blocks andother coded units, e.g., groups of pictures (GOPs). Storage media 28 maystore encoded video data received by input interface 26. Display device32 displays the decoded video data to a user, and may comprise any of avariety of display devices such as a cathode ray tube (CRT), a liquidcrystal display (LCD), a plasma display, an organic light emitting diode(OLED) display, or another type of display device.

Video encoder 22 and video decoder 30 each may be implemented as any ofa variety of suitable video encoder and/or video decoder circuitry, suchas one or more microprocessors, digital signal processors (DSPs),application specific integrated circuits (ASICs), field programmablegate arrays (FPGAs), discrete logic, software, hardware, firmware or anycombinations thereof. When the techniques are implemented partially insoftware, a device may store instructions for the software in asuitable, non-transitory computer-readable medium and execute theinstructions in hardware using one or more processors to perform thetechniques of this disclosure. Each of video encoder 22 and videodecoder 30 may be included in one or more encoders or decoders, eitherof which may be integrated as part of a combined CODEC in a respectivedevice.

In some examples, video encoder 22 and video decoder 30 may operateaccording to a video coding standard. Example video coding standardsinclude, but are not limited to, ITU-T H.261, ISO/IEC MPEG-1 Visual,ITU-T H.262 or ISO/IEC MPEG-2 Visual, ITU-T H.263, ISO/IEC MPEG-4 Visualand ITU-T H.264 (also known as ISO/IEC MPEG-4 AVC), including itsScalable Video Coding (SVC) and Multi-View Video Coding (MVC)extensions. In addition, a new video coding standard, namely HighEfficiency Video Coding (HEVC) or ITU-T H.265, including its range andscreen content coding extensions, 3D video coding (3D-HEVC) andmultiview extensions (MV-HEVC) and scalable extension (SHVC), has beendeveloped by the Joint Collaboration Team on Video Coding (JCT-VC) ofITU-T Video Coding Experts Group (VCEG) and ISO/IEC Motion PictureExperts Group (MPEG).

In other examples, video encoder 22 and video decoder 30 may beconfigured to operate according to other video coding techniques and/orstandards, including new video coding techniques being explored by theJoint Video Exploration Team (WET). In some examples of the disclosure,video encoder 22 and video decoder 30 may be configured to operateaccording to video coding techniques that use independent luma andchroma partitioning, such that luma and chroma blocks of video data arenot required to be aligned. Such partitioning techniques may lead to thesituation where a chroma block is not aligned, within a particularlocation of a picture, to a single luma block. In other examples of thedisclosure, video encoder 22 and video decoder 30 may be configured tooperate according to video coding techniques that use partitioningframeworks that allow for non-square blocks.

In accordance with the techniques of this disclosure, as will bedescribed in more detail below, video decoder 30 may be configured toreceive the bitstream of encoded video data, the encoded video datarepresenting partitioned luma blocks and partitioned chroma blocks,wherein the chroma blocks are partitioned independently of the lumablocks, determine a respective coding mode corresponding to therespective partitioned luma blocks, decode the respective partitionedluma blocks according the determined respective coding modes, decode afirst syntax element indicating that the respective coding modesassociated with the respective partitioned luma blocks are to be usedfor decoding a first partitioned chroma block, wherein the firstpartitioned chroma block is aligned with two or more partitioned lumablocks, determine a chroma coding mode for the first partitioned chromablock according to a function of the respective coding modes of the twoor more partitioned luma blocks, and decode the first partitioned chromablock in accordance with the determined chroma coding mode. Videoencoder 22 may be configured to perform techniques reciprocal to that ofvideo decoder 30. In some examples, video encoder 22 may be configuredto generate a syntax element that indicates whether or not a chromablock is to reuse coding mode information from two or more luma blocksbased the function of the respective coding modes of the two or morepartitioned luma blocks.

In HEVC and other video coding specifications, a video sequencetypically includes a series of pictures. Pictures may also be referredto as “frames.” A picture may include three sample arrays, denoted SL,Scb, and Scr. SL is a two-dimensional array (e.g., a block) of lumasamples. Scb is a two-dimensional array of Cb chrominance samples. Scris a two-dimensional array of Cr chrominance samples. Chrominancesamples may also be referred to herein as “chroma” samples. In otherinstances, a picture may be monochrome and may only include an array ofluma samples.

To generate an encoded representation of a picture (e.g., an encodedvideo bitstream), video encoder 22 may generate a set of coding treeunits (CTUs). Each of the CTUs may comprise a coding tree block of lumasamples, two corresponding coding tree blocks of chroma samples, andsyntax structures used to code the samples of the coding tree blocks. Inmonochrome pictures or pictures having three separate color planes, aCTU may comprise a single coding tree block and syntax structures usedto code the samples of the coding tree block. A coding tree block may bean N×N block of samples. A CTU may also be referred to as a “tree block”or a “largest coding unit” (LCU). The CTUs of HEVC may be broadlyanalogous to the macroblocks of other standards, such as H.264/AVC.However, a CTU is not necessarily limited to a particular size and mayinclude one or more coding units (CUs). A slice may include an integernumber of CTUs ordered consecutively in a raster scan order.

To generate a coded CTU, video encoder 22 may recursively performquadtree partitioning on the coding tree blocks of a CTU to divide thecoding tree blocks into coding blocks, hence the name “coding treeunits.” A coding block is an N×N block of samples. A CU may comprise acoding block of luma samples and two corresponding coding blocks ofchroma samples of a picture that has a luma sample array, a Cb samplearray, and a Cr sample array, and syntax structures used to code thesamples of the coding blocks. In monochrome pictures or pictures havingthree separate color planes, a CU may comprise a single coding block andsyntax structures used to code the samples of the coding block.

Video encoder 22 may partition a coding block of a CU into one or moreprediction blocks. A prediction block is a rectangular (i.e., square ornon-square) block of samples on which the same prediction is applied. Aprediction unit (PU) of a CU may comprise a prediction block of lumasamples, two corresponding prediction blocks of chroma samples, andsyntax structures used to predict the prediction blocks. In monochromepictures or pictures having three separate color planes, a PU maycomprise a single prediction block and syntax structures used to predictthe prediction block. Video encoder 22 may generate predictive blocks(e.g., luma, Cb, and Cr predictive blocks) for prediction blocks (e.g.,luma, Cb, and Cr prediction blocks) of each PU of the CU.

Video encoder 22 may use intra prediction or inter prediction togenerate the predictive blocks for a PU. If video encoder 22 uses intraprediction to generate the predictive blocks of a PU, video encoder 22may generate the predictive blocks of the PU based on decoded samples ofthe picture that includes the PU.

After video encoder 22 generates predictive blocks (e.g., luma, Cb, andCr predictive blocks) for one or more PUs of a CU, video encoder 22 maygenerate one or more residual blocks for the CU. As one example, videoencoder 22 may generate a luma residual block for the CU. Each sample inthe CU's luma residual block indicates a difference between a lumasample in one of the CU's predictive luma blocks and a correspondingsample in the CU's original luma coding block. In addition, videoencoder 22 may generate a Cb residual block for the CU. In one exampleof chroma prediction, each sample in the Cb residual block of a CU mayindicate a difference between a Cb sample in one of the CU's predictiveCb blocks and a corresponding sample in the CU's original Cb codingblock. Video encoder 22 may also generate a Cr residual block for theCU. Each sample in the CU's Cr residual block may indicate a differencebetween a Cr sample in one of the CU's predictive Cr blocks and acorresponding sample in the CU's original Cr coding block. However, itshould be understood that other techniques for chroma prediction may beused.

Furthermore, video encoder 22 may use quadtree partitioning to decomposethe residual blocks (e.g., the luma, Cb, and Cr residual blocks) of a CUinto one or more transform blocks (e.g., luma, Cb, and Cr transformblocks). A transform block is a rectangular (e.g., square or non-square)block of samples on which the same transform is applied. A transformunit (TU) of a CU may comprise a transform block of luma samples, twocorresponding transform blocks of chroma samples, and syntax structuresused to transform the transform block samples. Thus, each TU of a CU mayhave a luma transform block, a Cb transform block, and a Cr transformblock. The luma transform block of the TU may be a sub-block of the CU'sluma residual block. The Cb transform block may be a sub-block of theCU's Cb residual block. The Cr transform block may be a sub-block of theCU's Cr residual block. In monochrome pictures or pictures having threeseparate color planes, a TU may comprise a single transform block andsyntax structures used to transform the samples of the transform block.

Video encoder 22 may apply one or more transforms a transform block of aTU to generate a coefficient block for the TU. For instance, videoencoder 22 may apply one or more transforms to a luma transform block ofa TU to generate a luma coefficient block for the TU. A coefficientblock may be a two-dimensional array of transform coefficients. Atransform coefficient may be a scalar quantity. Video encoder 22 mayapply one or more transforms to a Cb transform block of a TU to generatea Cb coefficient block for the TU. Video encoder 22 may apply one ormore transforms to a Cr transform block of a TU to generate a Crcoefficient block for the TU.

After generating a coefficient block (e.g., a luma coefficient block, aCb coefficient block or a Cr coefficient block), video encoder 22 mayquantize the coefficient block. Quantization generally refers to aprocess in which transform coefficients are quantized to possibly reducethe amount of data used to represent the transform coefficients,providing further compression. After video encoder 22 quantizes acoefficient block, video encoder 22 may entropy encode syntax elementsindicating the quantized transform coefficients. For example, videoencoder 22 may perform context-adaptive binary arithmetic coding (CABAC)on the syntax elements indicating the quantized transform coefficients.

Video encoder 22 may output a bitstream that includes a sequence of bitsthat forms a representation of coded pictures and associated data. Thus,the bitstream comprises an encoded representation of video data. Thebitstream may comprise a sequence of network abstraction layer (NAL)units. A NAL unit is a syntax structure containing an indication of thetype of data in the NAL unit and bytes containing that data in the formof a raw byte sequence payload (RBSP) interspersed as necessary withemulation prevention bits. Each of the NAL units may include a NAL unitheader and encapsulates a RBSP. The NAL unit header may include a syntaxelement indicating a NAL unit type code. The NAL unit type codespecified by the NAL unit header of a NAL unit indicates the type of theNAL unit. A RBSP may be a syntax structure containing an integer numberof bytes that is encapsulated within a NAL unit. In some instances, anRB SP includes zero bits.

Video decoder 30 may receive an encoded video bitstream generated byvideo encoder 22. In addition, video decoder 30 may parse the bitstreamto obtain syntax elements from the bitstream. Video decoder 30 mayreconstruct the pictures of the video data based at least in part on thesyntax elements obtained from the bitstream. The process to reconstructthe video data may be generally reciprocal to the process performed byvideo encoder 22. For instance, video decoder 30 may use motion vectorsof PUs to determine predictive blocks for the PUs of a current CU. Inaddition, video decoder 30 may inverse quantize coefficient blocks ofTUs of the current CU. Video decoder 30 may perform inverse transformson the coefficient blocks to reconstruct transform blocks of the TUs ofthe current CU. Video decoder 30 may reconstruct the coding blocks ofthe current CU by adding the samples of the predictive blocks for PUs ofthe current CU to corresponding samples of the transform blocks of theTUs of the current CU. By reconstructing the coding blocks for each CUof a picture, video decoder 30 may reconstruct the picture.

In some example video codec frameworks, such as the quadtreepartitioning framework of HEVC, partitioning of video data into blocksfor the color components (e.g., luma blocks and chroma blocks) isperformed jointly. That is, in some examples, luma blocks and chromablocks are partitioned in the same manner such that no more than oneluma block corresponds to a chroma block in a particular location withina picture. In one example, a partition of a block of video data may befurther divided into sub-blocks. Information (e.g., sample values andsyntax elements indicating how the video block is to be coded) relatingto the video block or partition of the video block is stored at thesub-block level. Or, more generally, information relating to videoblocks or partitions of the video block may be stored with relation toone or more representative locations (e.g., corresponding to anysample(s) or sub-samples(s)) of a block of video data. For example, if apartition is 16×16 pixels, and each sub-block in the partition is 4×4pixels, then there are 16 sub-blocks in the partition. Information isstored at sub-block granularity, 4×4 in this example, and all 16sub-blocks may have the same information.

In the context of this disclosure, the terms “partition,” “block,” and“partitioned block” may be used interchangeably. In general, a block isa group of samples (e.g., luma or chroma samples) on which video codingis performed. In the context of this disclosure, a “sub-block” is adivision of a block having an associated memory location that storescoding mode information for the block.

Video encoder 22 and video decoder 30 may allocate locations in a memoryfor storing the information for each representative location (e.g.,sub-block). In some examples, the values of the information (e.g.,values of particular syntax elements for a particular coding mode) maybe stored in a separate memory location associated with eachrepresentative location (e.g., sub-block). In other examples, theinformation may be stored once for one of a plurality of representativelocations (e.g., sub-blocks) of a partition. The memory locations of theother sub-blocks of the partition may include pointers to the memorylocation that stores the actual values of the information. Techniques ofthis disclosure will be described below with reference to sub-blocks,though it should be understood that any representative location of ablock may be used.

As mentioned above, the information stored at the sub-block level can beany information that is used to perform coding processes on thepartition. Such information may be signaled syntax information orderived supplemental information. One example of derived supplementalinformation may be information used to code chroma blocks that isderived from information related to coding luma blocks. One example ofderived supplemental information for use in HEVC is direct modeinformation, where luma intra prediction information (e.g., intraprediction direction) is used for chroma prediction without signalingthe intra prediction direction itself for chroma blocks. Other examplesof the information may be mode decision, such as intra prediction orinter prediction, intra prediction direction, motion information, andthe like.

When luma and chroma partition sizes are compared, chroma color format(e.g., chroma sub-sampling format), such as 4:4:4, 4:2:2, 4:2:0, can betaken into the account. For example, if a luma partition is 16×16pixels, the corresponding or collocated chroma partition is 8×8 pixelsfor the 4:2:0 color format, and is 16×16 pixels for the 4:4:4 chromacolor format. Partitions are not necessarily square, and can be, forexample, rectangular in shape. As such, for a 4:2:0 chroma sub-samplingformat, luma and chroma partitions will not be the same size. However,when luma and chroma blocks are partitioned jointly, the resultingpartitioning still results in only one luma block corresponding to anyparticular chroma block.

A quadtree plus binary tree (QTBT) partition structure is currentlybeing studied by the Joint Video Exploration Team (WET). In J. An etal., “Block partitioning structure for next generation video coding”,International Telecommunication Union, COM16-C966, September 2015(hereinafter, “VCEG proposal COM16-C966”), QTBT partitioning techniqueswere described for future video coding standard beyond HEVC. Simulationshave shown that the proposed QTBT structure may be more efficient thanthe quadtree structure used in HEVC.

In the QTBT structure described in VCEG proposal COM16-C966, a CTB isfirst partitioned using quadtree partitioning techniques, where thequadtree splitting of one node can be iterated until the node reachesthe minimum allowed quadtree leaf node size. The minimum allowedquadtree leaf node size may be indicated to video decoder 30 by thevalue of the syntax element MinQTSize. If the quadtree leaf node size isnot larger than the maximum allowed binary tree root node size (e.g., asdenoted by a syntax element MaxBTSize), the quadtree leaf node can befurther partitioned using binary tree partitioning. The binary treepartitioning of one node can be iterated until the node reaches theminimum allowed binary tree leaf node size (e.g., as denoted by a syntaxelement MinBTSize) or the maximum allowed binary tree depth (e.g., asdenoted by a syntax element MaxBTDepth). VCEG proposal COM16-C966 usesthe term “CU” to refer to binary-tree leaf nodes. In VCEG proposalCOM16-C966, CUs are used for prediction (e.g., intra prediction, interprediction, etc.) and transform without any further partitioning. Ingeneral, according to QTBT techniques, there are two splitting types forbinary tree splitting: symmetric horizontal splitting and symmetricvertical splitting. In each case, a block is split by dividing the blockdown the middle, either horizontally or vertically. This differs fromquadtree partitioning, which divides a block into four blocks.

In one example of the QTBT partitioning structure, the CTU size is setas 128×128 (e.g., a 128×128 luma block and two corresponding 64×64chroma blocks), the MinQTSize is set as 16×16, the MaxBTSize is set as64×64, the MinBTSize (for both width and height) is set as 4, and theMaxBTDepth is set as 4. Quadtree partitioning is applied to the CTUfirst to generate quadtree leaf nodes. The quadtree leaf nodes may havea size from 16×16 (i.e., the MinQTSize is 16×16) to 128×128 (i.e., theCTU size). According to one example of QTBT partitioning, if the leafquadtree node is 128×128, the leaf quadtree node cannot be further splitby the binary tree, since the size of the leaf quadtree node exceeds theMaxBTSize (i.e., 64×64). Otherwise, the leaf quadtree node is furtherpartitioned by the binary tree. Therefore, the quadtree leaf node isalso the root node for the binary tree and has the binary tree depth as0. The binary tree depth reaching MaxBTDepth (e.g., 4) implies thatthere is no further splitting. The binary tree node having a width equalto the MinBTSize (e.g., 4) implies that there is no further horizontalsplitting. Similarly, the binary tree node having a height equal toMinBTSize implies no further vertical splitting. The leaf nodes of thebinary tree (CUs) are further processed (e.g., by performing aprediction process and a transform process) without any furtherpartitioning.

FIG. 2A illustrates an example of a block 50 (e.g., a CTB) partitionedusing QTBT partitioning techniques. As shown in FIG. 2A, using QTBTpartition techniques, each of the resultant blocks is splitsymmetrically through the center of each block. FIG. 2B illustrates thetree structure corresponding to the block partitioning of FIG. 2A. Thesolid lines in FIG. 2B indicate quadtree splitting and dotted linesindicate binary tree splitting. In one example, in each splitting (i.e.,non-leaf) node of the binary tree, a syntax element (e.g., a flag) issignaled to indicate the type of splitting performed (e.g., horizontalor vertical), where 0 indicates horizontal splitting and 1 indicatesvertical splitting. For the quadtree splitting, there is no need toindicate the splitting type, as quadtree splitting always splits a blockhorizontally and vertically into 4 sub-blocks with an equal size.

As shown in FIG. 2B, at node 70, block 50 is split into the four blocks51, 52, 53, and 54, shown in FIG. 2A, using quadtree partitioning. Block54 is not further split, and is therefore a leaf node. At node 72, block51 is further split into two blocks using binary tree partitioning. Asshown in FIG. 2B, node 72 is marked with a 1, indicating verticalsplitting. As such, the splitting at node 72 results in block 57 and theblock including both blocks 55 and 56. Blocks 55 and 56 are created by afurther vertical splitting at node 74. At node 76, block 52 is furthersplit into two blocks 58 and 59 using binary tree partitioning. As shownin FIG. 2B, node 76 is marked with a 1, indicating horizontal splitting.

At node 78, block 53 is split into 4 equal size blocks using quadtreepartitioning. Blocks 63 and 66 are created from this quadtreepartitioning and are not further split. At node 80, the upper left blockis first split using vertical binary tree splitting resulting in block60 and a right vertical block. The right vertical block is then splitusing horizontal binary tree splitting into blocks 61 and 62. The lowerright block created from the quadtree splitting at node 78, is split atnode 84 using horizontal binary tree splitting into blocks 64 and 65.

In one example of QTBT partitioning, luma and chroma partitioning may beperformed independently of each other for I-slices, contrary, forexample, to HEVC, where the quadtree partitioning is performed jointlyfor luma and chroma blocks. That is, in some examples being studied,luma blocks and chroma blocks may be partitioned separately such thatluma blocks and chroma blocks do not directly overlap. As such, in someexamples of QTBT partitioning, chroma blocks may be partitioned in amanner such that at least one partitioned chroma block is not spatiallyaligned with a single partitioned luma block. That is, the luma samplesthat are co-located with a particular chroma block may be within two ormore different luma partitions.

As described above, in some examples, information relating to how achroma block is to be coded can be derived from information relating toa corresponding luma block. However if luma and chroma partitioning isperformed independently, the luma and chroma blocks may not be aligned(e.g., the luma and chroma blocks may not correspond to the same set ofpixels). For example, chroma partitioning can be such that the chromablocks are larger or smaller than a corresponding luma partition. Inaddition, chroma blocks may spatially overlap two or more luma blocks.As explained above, if a partitioned chroma block is larger than apartitioned luma block, it can be the case than there is more than oneluma block that spatially corresponds to a particular chroma block, andthus more than one set of luma information (e.g., syntax elements andthe like) associated with the luma partitions corresponding to the sizeof the chroma partition. In such cases, it is unclear how to derivechroma information from luma information. It should be understood thatsuch a situation may arise with any partitioning structure where lumaand chroma blocks are partitioned independently, and not just withexample QTBT partitioning structures being studied by the JVET.

In view of these drawbacks, this disclosure describes methods anddevices for deriving chroma information from luma information forpictures partitioned using separate and/or independent luma and chromapartitioning. As described above, luma and chroma partitioning can bemisaligned, e.g., being of different sizes or shapes. Derivedinformation (e.g., determined coding mode information) from a luma blockcan be used as a predictor for chroma information (e.g., the coding modeto be used for a chroma block) or be used to code a chroma block ofvideo data. Alternatively or additionally, luma information can be usedfor context modelling in the context coding of the chroma information.Optionally, context modelling can be combined with the predictioninformation. It should be understood that each of the techniquesdescribed below may be used independently or may be combined with theother techniques in any combination.

As one example of the disclosure, video encoder 22 encodes a luma blockof video data using a particular coding mode (e.g., a particular intraprediction mode, a particular inter prediction mode, a particularfiltering mode, a particular motion vector prediction mode, etc.). Insome examples, video encoder 22 may further encode syntax elements thatindicate what coding mode(s) were used to encode a particular lumablock. Video decoder 30 may be configured to decode the syntax elementsto determine the coding mode(s) to use to decode the luma block. Inother examples, video decoder 30 may not receive syntax elements thatexplicitly indicate a particular coding mode. Rather, video decoder 30may be configured to derive a particular coding mode for a luma blockbased on various video characteristics (e.g., block size, informationfrom neighboring blocks, etc.) and a set of predetermined rules. Inother examples, video decoder 30 may determine coding modes based on acombination of explicitly signaled syntax elements and predeterminedrules.

In one example, video encoder 22 may optionally encode chroma blocks(e.g., a Cr block and/or a Cb block) using the same coding mode as acorresponding luma block. Rather than video encoder 22 simply signalingsyntax elements and/or other information indicating the coding mode forthe chroma blocks, video encoder 22 may signal a syntax element (e.g., aflag) that indicates to video decoder 30 to reuse any signaled orderived information for determining the coding mode(s) for the lumablock as a predictor for the coding mode(s) of one or more correspondingchroma blocks. For example, a flag may be coded for one or more chromablocks to indicate whether the chroma blocks are coded with the samecoding mode as a corresponding luma block. If not, than video encoder 22generates syntax elements indicating the coding mode for the chromablock independently, where video encoder 22 can take into account thatthe chroma mode is not equal to the luma mode. That is, video encoder 22and video decoder may be able to determine that the coding mode for thechroma block is not the same as the coding mode for the luma block, andtherefore, the coding mode for the luma block can be excluded as apossibility for the chroma block. In a further example, a separatecontext can be used to code the flag that indicates whether chromacomponent is coded using the same mode as the luma component.

In the example describe above, it is assumed video encoder 22 and videodecoder 30 code the luma block first, followed by coding the one or morechroma blocks. In this example, luma information is already availablewhen a chroma block is being coded. If video encoder 22 and videodecoder 30 are configured to code the blocks in another order (e.g., achroma block is coded first), then luma and chroma terms can be simplybe swapped in the following examples.

In one example of the disclosure, video decoder 30 may be configured toreceive a bitstream of encoded video data and store the encoded videodata in a memory (e.g., storage media 28 of FIG. 1). The encoded videodata may represent both partitioned luma blocks and partitioned chromablocks. In some examples, the partitioned chroma blocks may include bothCr chroma blocks and Cb chroma blocks. As used in the disclosure, theterm “chroma block” may refer to any type of block that includes anytype of chroma information. In the examples of this disclosure, thechroma blocks are partitioned independently of the luma blocks. That is,video encoder 22 may be configured to encode the video data using aseparate partitioning structure for luma blocks and chroma blocks.

Such a separate partitioning structure may result in at least onepartitioned chroma block not being aligned with a single partitionedluma block. As such, for a particular spatial location of a picture,video encoder 22 may partition a single chroma block, but partitionmultiple luma blocks. However, it should be understood that for otherspatial locations of the picture, there may be a 1 to 1 correspondencebetween luma and chroma blocks, or there may be multiple chroma blocksfor a single luma block. The QTBT partitioning structure described aboveis a type of partitioning structure where luma and chroma blocks arepartitioned independently/separately. However, the techniques of thisdisclosure may be applied to video data partitioned according to anypartitioning structure where luma and chroma blocks are partitionedindependently.

Video decoder 30 may be further configured to determine a coding modefor the respective partitioned luma blocks received in the encoded videobitstream and decode the respective partitioned luma blocks accordingthe determined respective coding modes. Video decoder 30 may beconfigured to determine the coding mode from information indicated bysyntax elements received in the encoded video bitstream. Such syntaxelements may indicate the coding modes explicitly. In other examples,video decoder 30 may be configured to implicitly determine the codingmode for the luma blocks from characteristics of the video data and somepredetermined rules. In other examples, video decoder 30 may determinethe coding modes for the luma blocks using a combination of explicitlysignaled syntax elements and implicitly determined coding modes frompredetermined rules and video data characteristics.

In the context of this disclosure, the coding modes can be anyinformation that indicates to video decoder 30 how video encoder 22encoded the encoded video data, and how video decoder 30 should decodethe video data. Example coding modes may include direct mode for chromaintra prediction, a position-dependent intra prediction combination(PDPC) flag (e.g., indicating if a PDPC mode is used), PDPC parameters,secondary transform sets for a non-separable secondary transforms(NSST), enhanced multiple transform (EMT), adaptive multiple transforms(AMT), and contexts for selecting entropy coding data models. The aboveare examples of chroma coding modes that can be derived from the lumacoding modes (coding modes used to code luma blocks) determined by videodecoder 30, and which have been used in the JEM test model studied inJVET. However, it should be understood that the coding modes may includeany coding mode used for coding the luma blocks that may be reused forcoding chroma blocks or used to predict the coding mode for a chromablock.

Regardless of the type of coding mode, or the manner in which the codingmode was determined, video decoder 30 may be configured to store thedetermined coding mode for a particular partitioned luma blocks in aplurality of different memory locations associated with the particularpartitioned luma block. As will be explained in more detail below withreference to FIG. 3, a particular partitioned luma block may be dividedinto sub-blocks, and video decoder 30 may store the coding modedetermined for the entire particular partitioned luma block in memorylocations corresponding to each of the sub-blocks. Accordingly, for aparticular partitioned luma block divided into N sub-blocks, the codingmode is stored in N different memory locations, each memory locationcorresponding to a particular spatially located sub-block within thepartitioned luma block. Sub-blocks can be a rectangular or square blockof any size. In some examples, a sub-block may be just one sample, i.e.,a block of size of 1×1. In some examples, each memory location may storedata that explicitly indicates the coding mode for the particularpartitioned luma block. In other examples, one or more memory locationassociated with the particular partitioned luma block explicitly storesinformation indicating the coding mode, while the other memory locationsassociated with the particular partitioned luma block store pointers tothe memory location(s) that explicitly stores the coding mode.

According to some examples of the disclosure, video decoder 30 may beconfigured to reuse coding mode information received for a luma blockfor use when decoding a chroma block. In some examples, video decoder 30may receive and decode a first syntax element indicating if coding modesassociated with the respective partitioned luma blocks are to be usedfor decoding a particular partitioned chroma block. As described above,a partitioned chroma block may be spatially aligned with two or moredifferent partitioned luma blocks. As such, it may be difficult todetermine how to reuse luma coding modes for such a chroma block, as itis unclear from which luma block to inherit (e.g., reuse) the codingmode information. By storing the luma coding mode information inmultiple memory locations corresponding to multiple sub-block locations,video decoder 30 may be configured to determine which coding modeinformation from the luma block to reuse for a particular chroma blockusing a function of the coding mode information stored for sub-blocksthat correspond to the spatial location of the particular chroma block.In this context, the function may be a set of predetermined rules andanalysis techniques that video decoder 30 uses to determine which codingmode(s) of the two or more co-located partitioned luma blocks to reusefor the partitioned chroma block. Once the luma coding mode to reuse isdetermined, video decoder 30 may decode the particular partitionedchroma block with the determined coding mode.

Video decoder 30 may be configured to determine which coding mode toreuse from two or more spatially aligned luma blocks based on a functionof coding mode information stored in memory locations associated withsub-blocks of the partitioned luma blocks. Several different functionsmay be used. In one example of the disclosure, video decoder 30 may beconfigured to perform a statistical analysis of the luma coding modeinformation corresponding to the two or more luma partitions that arecollocated with chroma partition. The determined luma coding modeinformation from the luma block for use by the chroma block may be afunction of the whole luma coding mode information (e.g., the codingmode information contained in every luma sub-block that is co-locatedwith the chroma block) and how luma coding mode information varies(e.g., to what extent the information is similar or different) acrossthe co-located sub-blocks in the luma block. One difference from theprevious techniques for coding mode reuse and the techniques of thisdisclosure, is that the luma coding mode information can be related tomore than one luma block (or partition) due to the separate luma andchroma partitioning.

Examples of a function that may be used for determining what luma codingmode information from two or more partitioned luma blocks can be reusedfor a co-located chroma block may include, but is not limited to, one ormore of the functions described below. In one example, video decoder 30may perform a function that includes a statistical analysis of thecoding mode information indicating the determined respective coding modeof two or more partitioned luma blocks. The coding mode information isstored in respective memory locations associated with the respectivesub-blocks of the two or more partitioned luma blocks. In one example,video decoder 30 may analyze the coding mode information and return(e.g., to determine to use and obtain from memory) the coding modeinformation that appears most often for the co-located sub-blocks of thetwo or more partitioned luma blocks. That is, the function returns themajority of the luma information used in the corresponding luma blocks.In this manner, the function indicates that particular luma coding modeinformation, from two or more partitioned luma blocks, to be reused fora co-located chroma block.

In other examples, video decoder 30 may use a function performs ananalysis of the coding mode information for the sub-blocks of the two ormore partitioned luma blocks, the analysis includes measuring thegradient or higher derivatives of the luma coding mode information tomeasure the smoothness of that information. For example, some extreme(e.g., outlier) coding mode information in the two or more luma blocks,which may be much different from the majority of the coding modeinformation related to the two or more luma blocks, can be ignored andnot reused for the chroma blocks. In other examples, video decoder 30may assign different weights to the luma coding mode information storedfor respective sub-blocks, and use a weighted average of coding modes todetermine which mode to reuse for the chroma block. The weights may beassigned based on the relative locations of the luma sub-blocks that areco-located with the chroma block.

In other examples, the functions used to determine what luma codingmode(s) to reuse for a chroma block may include one or more of thefollowing video coding characteristics. The functions video decoder 30may use to determine what luma coding mode(s) to reuse for a chromablock may include the shape of the block (rectangular, square), a blockorientation (vertical or horizontal oriented rectangular block), a shapeof the chroma block, a shape of the luma block containing representativelocation, the width or height of the luma and/or chroma blocks, morefrequently used luma mode of the area corresponding to the chroma block.In other examples, the function may be based on the prediction mode orluma information in the representative location. For example, if videodecoder 30 is configured to reuse a luma intra mode for a chroma block,but the luma block in the representative location is coded with an intermode, video decoder 30 may configured to select another representativelocation to determine the luma intra mode to reuse for the chroma block.More generally, if video decoder 30 is determine what luma informationto reuse to code a chroma block, but the luma information may not bevalid for this chroma block, video decoder 30 may consider lumainformation from another representative location in the luma block, orotherwise may use some default luma information.

In another example of the disclosure, video decoder 30 may reuse codingmode information based on a predetermined sub-block location. Forexample, video decoder 30 may simply reuse the coding mode informationstored for a particular sub-block location that is co-located with thechroma block. As one example, video decoder 30 may reuse coding modeinformation stored at a luma sub-block that is co-located with aparticular corner of the partitioned chroma block. Any corner sub-blockmay be used. As another example, video decoder 30 may reuse coding modeinformation stored at a luma sub-block that is co-located with a centerof the partitioned chroma block. In other examples, video decoder 30 mayperform a statistical analysis (e.g., as described above) of the codingmode information stored for some predetermined number of luma sub-blocklocations. That is, video decoder 30 may use a function that analyzescertain sub-blocks of a luma partition and derives chroma informationbased on the luma information contained therein.

In another example, video decoder 30 may divide the partitioned chromablock into multiples of sub-blocks, e.g., 1×1, 2×2, 4×4, or other sizedsub-blocks. Then, for each sub-block, video decoder 30 may inherit(e.g., reuse) the luma coding mode information stored for a particularluma sub-block for a co-located chroma sub-block. In this way, differentcoding information from the corresponding luma block can be applied in asingle chroma block.

As discussed above, video decoder 30 may use one of a plurality ofpredetermined functions for determining how to reuse luma coding modeinformation for chroma blocks. In some examples, video decoder 30 may beconfigured to use a single predetermined function, and use that functionfor all pictures. In other examples, video decoder 30 may determinewhich function to use based on some video coding characteristics. Inother examples, video encoder 22 may be configured to signal a syntaxelement that indicates to video decoder 30 what function to use todetermine how to reuse luma coding mode information. Such a syntaxelement may be signaled at any level, e.g., a sequence level, a picturelevel, a slice level, a tile level, a CTB level, etc.

FIG. 3 is a conceptual diagram illustrating an example of luma andchroma relative partitioning in accordance with the techniques of thisdisclosure. As shown in FIG. 3, information is stored per partition(e.g., partitioned luma blocks) in sub-blocks of the partitions (dashedboxes). The sub-blocks may be of any size, down to the size of anindividual sample. FIG. 3 shows that one chroma partition, whether in a4:4:4 or 4:2:0 sub-sampling format, may have more than one associatedluma partition. As such, a single chroma partition may have more thanone corresponding set of luma information. Certain representativelocations (e.g., sub-blocks) of the luma partitions may be used toanalyze the luma information (e.g., coding modes) so as to derive thechroma information for the corresponding chroma partition, as describedabove.

FIG. 4 is a conceptual diagram illustrating another example of luma andchroma relative partitioning in accordance with the techniques of thisdisclosure. As shown in FIG. 4, information is stored per partition insub-blocks (dashed boxes) of the luma partition. FIG. 4 shows that eachsub-block in one chroma partition may have one associated lumasub-block, and the luma information of the associated one luma sub-blockcan be analyzed to derive the chroma information for the correspondingchroma sub-block.

The following section describes some examples that may use thetechniques of the disclosure. In chroma direct mode, the luma intradirection is used for chroma intra prediction. An example of this modewas used in HEVC. In accordance with one example technique of thisdisclosure, when the chroma and luma structure is not aligned (e.g., dueto independent chroma and luma partitioning), the center representativeluma sub-block is selected to obtain the luma intra prediction mode,which is then applied for the chroma partition as the direct mode. Otherluma sub-blocks of the corresponding luma partition may have other intradirections different from the selected sub-block. Other functionsinstead of using the center representative sub-block, as explainedabove, may also be used.

In another example, in chroma direct mode, when the chroma and lumastructure is not aligned, the chroma intra prediction is performed in2×2 (or 4×4) sub-block units. For each 2×2 (or 4×4) chroma sub-block,one associated 4×4 luma sub-block is identified, and the intraprediction mode of this identified 4×4 luma sub-block is applied for thecurrent chroma 2×2 (or 4×4) sub-block.

In another example, a chroma PDPC control flag (i.e., PDPC mode isapplied or not) and PDPC parameters are derived, for example, from thecenter representative luma sub-block, and applied for the chromapartition. Other functions instead of using the center representativesub-block, as explained above, may also be used.

In another example, a secondary transform (NSST) set is selected byvideo decoder 30 from the center representative luma sub-block and isapplied for the chroma partition. Other functions instead of using thecenter representative sub-block, as explained above, may also be used.

Similar techniques may be applied by video decoder 30 to any chromainformation that is derived from luma information.

The foregoing examples were described with reference to video decoder30. However, video encoder 22 may employ the same techniques fordetermining how to reuse information generated, derived, and/or signaledfor luma blocks for chroma blocks. In particular, video encoder 22 maydetermine whether or not to signal a syntax element that indicateswhether or not luma coding mode information should be reused for chromablocks based on the function the video decoder will use to determinewhat luma coding mode information to reuse.

The following sections describes techniques for determining parametersfor a position-dependent intra prediction combination (PDPC) coding modefor blocks of video data that may be partitioned into non-square,rectangular partitions. The QTBT partitioning structure described aboveis an example of a partitioning structure that allows for non-square,rectangular blocks. However, the techniques of this disclosure may beused with any partitioning structure that produces non-square,rectangular blocks.

When coding video data using the PDPC coding mode, video encoder 22and/or video decoder 30 may use one or more parameterized equations thatdefine how to combine predictions based on filtered and unfilteredreference values and based on the position of the predicted pixel. Thepresent disclosure describes several sets of parameters, such that videoencoder 22 may be configured to test the sets of parameters (via, e.g.,using rate-distortion analysis) and signal to video decoder 30 theoptimal parameters (e.g., the parameters resulting in the bestrate-distortion performance among those parameters that are tested). Inother examples, video decoder 30 may be configured to determine PDPCparameters from characteristics of the video data (e.g., block size,block height, block width, etc.).

FIG. 5A illustrates a prediction of a 4×4 block (p) using an unfilteredreference (r) according to techniques of the present disclosure. FIG. 5Billustrates a prediction of a 4×4 block (q) using a filtered reference(s) according to techniques of the present disclosure. While both FIGS.5A and 5B illustrate a 4×4 pixel block and 17 (4×4+1) respectivereference values, the techniques of the present disclosure may beapplied to any block size and number of reference values.

Video encoder 22 and/or video decoder 30, when performing the PDPCcoding mode, may utilize a combination between the filtered (q) andunfiltered (p) predictions, such that a predicted block for a currentblock to be coded can be computed using pixel values from both thefiltered (s) and unfiltered (r) reference arrays.

In one example of the techniques of PDPC, given any two set of pixelpredictions p_(r)[x, y] and q_(s) [x, y], computed using only theunfiltered and filtered references r and s, respectively, the combinedpredicted value of a pixel, denoted by v[x, y], is defined byv[x,y]=c[x,y]p _(r)[x,y]+(1−c[x,y])q _(s)[x,y]  (1)where c[x, y] is the set of combination parameters. The value of theweight c[x, y] may be a value between 0 and 1. The sum of the weightsc[x, y] and (1−c[x, y]) may be equal to one.

In certain examples it may not be practical to have a set of parametersas large as the number of pixels in the block. In such examples c[x, y]may be defined by a much smaller set of parameters, plus an equation tocompute all combination values from those parameters. In such an examplethe following formula may be used:

$\begin{matrix}{{v\left\lbrack {x,y} \right\rbrack} = {\left\lfloor \frac{{c_{1}^{(v)}{r\left\lbrack {x,{- 1}} \right\rbrack}} - {c_{2}^{(v)}{r\left\lbrack {{- 1},{- 1}} \right\rbrack}}}{2^{\lfloor\frac{y}{d_{v}}\rfloor}} \right\rfloor + \left\lfloor \frac{{c_{1}^{(h)}{r\left\lbrack {{- 1},y} \right\rbrack}} - {c_{2}^{(h)}{r\left\lbrack {{- 1},{- 1}} \right\rbrack}}}{2^{\lfloor\frac{x}{d_{h}}\rfloor}} \right\rfloor + {\left( \frac{N - {\min\left( {x,y} \right)}}{N} \right){{gp}_{r}^{({HEVC})}\left\lbrack {x,y} \right\rbrack}} + {{b\left\lbrack {x,y} \right\rbrack}{q_{s}^{({HEVC})}\left\lbrack {x,y} \right\rbrack}}}} & (2)\end{matrix}$where c₁ ^(v), c₂ ^(v), c₁ ^(h), c₂ ^(h), g, and d_(v), d_(h) ∈{1,2},are prediction parameters, N is the block size, p_(r)[x, y] andq_(s)[x,y] are prediction values computed using the according to theHEVC standard, for the specific mode, using respectively the nonfilteredand filtered references, and

$\begin{matrix}{{b\left\lbrack {x,y} \right\rbrack} = {1 - \left\lfloor \frac{c_{1}^{(v)} - c_{2}^{(v)}}{2^{\lfloor{y/d_{v}}\rfloor}} \right\rfloor - \left\lfloor \frac{c_{1}^{(h)} - c_{2}^{(h)}}{2^{\lfloor{x/d_{h}}\rfloor}} \right\rfloor - {\left( \frac{N - {\min\left( {x,y} \right)}}{N} \right)g}}} & (3)\end{matrix}$is a normalization factor (i.e., to make the overall weights assigned top_(r) ^((HEVC))[x, y] and q_(s) ^((HEVC))[x,y] add to 1), defined by theprediction parameters.

Formula 2 may be generalized for any video coding standard in formula2A:

$\begin{matrix}{{v\left\lbrack {x,y} \right\rbrack} = {\left\lfloor \frac{{c_{1}^{(v)}{r\left\lbrack {x,{- 1}} \right\rbrack}} - {c_{2}^{(v)}{r\left\lbrack {{- 1},{- 1}} \right\rbrack}}}{2^{\lfloor\frac{y}{d_{v}}\rfloor}} \right\rfloor + \left\lfloor \frac{{c_{1}^{(h)}{r\left\lbrack {{- 1},y} \right\rbrack}} - {c_{2}^{(h)}{r\left\lbrack {{- 1},{- 1}} \right\rbrack}}}{2^{\lfloor\frac{x}{d_{h}}\rfloor}} \right\rfloor + {\left( \frac{N - {\min\left( {x,y} \right)}}{N} \right){{gp}_{r}^{({STD})}\left\lbrack {x,y} \right\rbrack}} + {{b\left\lbrack {x,y} \right\rbrack}{q_{s}^{({STD})}\left\lbrack {x,y} \right\rbrack}}}} & \left( {2A} \right)\end{matrix}$where c₁ ^(v), c₂ ^(v), c₁ ^(h), c₂ ^(h), g, and d_(v), d_(h) ∈{1,2},are prediction parameters, N is the block size, p_(r) ^((STD))[x, y] andq_(s) ^(STD)[x,y] are prediction values computed using the according toa video coding standard (or video coding scheme or algorithm), for thespecific mode, using respectively the nonfiltered and filteredreferences, and

$\begin{matrix}{{b\left\lbrack {x,y} \right\rbrack} = {1 - \left\lfloor \frac{c_{1}^{(v)} - c_{2}^{(v)}}{2^{\lfloor{y/d_{v}}\rfloor}} \right\rfloor - \left\lfloor \frac{c_{1}^{(h)} - c_{2}^{(h)}}{2^{\lfloor{x/d_{h}}\rfloor}} \right\rfloor - {\left( \frac{N - {\min\left( {x,y} \right)}}{N} \right)g}}} & \left( {3A} \right)\end{matrix}$

-   -   is a normalization factor (i.e., to make the overall weights        assigned to p_(r) ^((STD))[x, y] and q_(s) ^((STD))[x,y] add to        1), defined by the prediction parameters.

These prediction parameters may include weights to provide an optimallinear combination of the predicted terms according to the type ofprediction mode used (e.g., DC, planar, and 33 directional modes ofHEVC). For example, HEVC contains 35 prediction modes. A lookup tablemay be constructed with values for each of the prediction parameters c₁^(v), c₂ ^(v), c₁ ^(h), c₂ ^(h), g, d_(v), and d_(h) for each of theprediction modes (i.e., 35 values of c₁ ^(v), c₂ ^(v), c₁ ^(h), c₂ ^(h),g, d_(v), and d_(h) for each prediction mode). Such values may beencoded in a bitstream with the video or may be constant values known bythe encoder and decoder ahead of time and may not need to be transmittedin a file or bitstream. The values for c₁ ^(v), c₂ ^(v), c₁ ^(h), c₂^(h), g, d_(v), and d_(h) may be determined by an optimization trainingalgorithm by finding the values for the prediction parameters that givebest compression for a set of training videos.

In another example, there are a plurality of predefined predictionparameter sets for each prediction mode (in e.g. a lookup table) and theprediction parameter set selected (but not the parameters themselves) istransmitted to a decoder in an encoded file or bitstream. In anotherexample the values for c₁ ^(v), c₂ ^(v), c₁ ^(h), c₂ ^(h), g, d_(v), andd_(h) may be generated on the fly by a video encoder and transmitted toa decoder in an encoded file or bitstream.

In another example, instead of using HEVC prediction, a video codingdevice performing these techniques may use a modified version of HEVC,like one that uses 65 directional predictions instead of 33 directionalpredictions. In fact, any type of intra-frame prediction can be used.

In another example, the formula can be chosen to facilitatecomputations. For example, we can use the following type of predictor

$\begin{matrix}{{v\left\lbrack {x,y} \right\rbrack} = {\left\lfloor \frac{{c_{1}^{(v)}{r\left\lbrack {x,{- 1}} \right\rbrack}} - {c_{2}^{(v)}{r\left\lbrack {{- 1},{- 1}} \right\rbrack}}}{2^{\lfloor{y/d_{v}}\rfloor}} \right\rfloor + \left\lfloor \frac{{c_{1}^{(h)}{r\left\lbrack {{- 1},y} \right\rbrack}} - {c_{2}^{(h)}{r\left\lbrack {{- 1},{- 1}} \right\rbrack}}}{2^{\lfloor{x/d_{h}}\rfloor}} \right\rfloor + {{b\left\lbrack {x,y} \right\rbrack}{p_{a,r,s}^{({HEVC})}\left\lbrack {x,y} \right\rbrack}\mspace{14mu}{where}}}} & (4) \\{\mspace{79mu}{{b\left\lbrack {x,y} \right\rbrack} = {1 - \left\lfloor \frac{c_{1}^{(v)} - c_{2}^{(v)}}{2^{\lfloor{y/d_{v}}\rfloor}} \right\rfloor - {\left\lfloor \frac{c_{1}^{(h)} - c_{2}^{(h)}}{2^{\lfloor{x/d_{h}}\rfloor}} \right\rfloor\mspace{14mu}{and}}}}} & (5) \\{\mspace{79mu}{{p_{a,r,s}^{({HEVC})}\left\lbrack {x,y} \right\rbrack} = {{{ap}_{r}^{({HEVC})}\left\lbrack {x,y} \right\rbrack} + {\left( {1 - a} \right){{q_{s}^{({HEVC})}\left\lbrack {x,y} \right\rbrack}.}}}}} & (6)\end{matrix}$

Such an approach may exploit the linearity of the HEVC (or other)prediction. Defining h as the impulse response of a filter k from apredefined set, if we haves=ar+(1−a)(h*r)  (7)

-   -   where “*” represents convolution, then        p _(a,r,s) ^((HEVC))[x,y]=p _(s) ^((HEVC))[x,y]  (8)    -   i.e., the linearly combined prediction may be computed from the        linearly combined reference.

Formulas 4, 6 and 8 may be may be generalized for any video codingstandard in formula 4A, 6A, and 8A:

$\begin{matrix}{{v\left\lbrack {x,y} \right\rbrack} = {\left\lfloor \frac{{c_{1}^{(v)}{r\left\lbrack {x,{- 1}} \right\rbrack}} - {c_{2}^{(v)}{r\left\lbrack {{- 1},{- 1}} \right\rbrack}}}{2^{\lfloor{y/d_{v}}\rfloor}} \right\rfloor + \left\lfloor \frac{{c_{1}^{(h)}{r\left\lbrack {{- 1},y} \right\rbrack}} - {c_{2}^{(h)}{r\left\lbrack {{- 1},{- 1}} \right\rbrack}}}{2^{\lfloor{x/d_{h}}\rfloor}} \right\rfloor + {{b\left\lbrack {x,y} \right\rbrack}{p_{a,r,s}^{({STD})}\left\lbrack {x,y} \right\rbrack}\mspace{14mu}{where}}}} & \left( {4A} \right) \\{\mspace{79mu}{{b\left\lbrack {x,y} \right\rbrack} = {1 - \left\lfloor \frac{c_{1}^{(v)} - c_{2}^{(v)}}{2^{\lfloor{y/d_{v}}\rfloor}} \right\rfloor - {\left\lfloor \frac{c_{1}^{(h)} - c_{2}^{(h)}}{2^{\lfloor{x/d_{h}}\rfloor}} \right\rfloor\mspace{14mu}{and}}}}} & \left( {5A} \right) \\{\mspace{79mu}{{p_{a,r,s}^{({STD})}\left\lbrack {x,y} \right\rbrack} = {{{ap}_{r}^{({STD})}\left\lbrack {x,y} \right\rbrack} + {\left( {1 - a} \right){{q_{s}^{({STD})}\left\lbrack {x,y} \right\rbrack}.}}}}} & \left( {6A} \right)\end{matrix}$

-   -   Such an approach may exploit the linearity of the prediction of        the coding standard. Defining h as the impulse response of a        filter k from a predefined set, if we have        s=ar+(1−a)(h*r)  (7A)    -   where “*” represents convolution, then        p _(a,r,s) ^((STD))[x,y]=p _(s) ^((STD))[x,y]  (8A)    -   i.e., the linearly combined prediction may be computed from the        linearly combined reference.

In an example, prediction functions may use the reference vector (e.g.,r and s) only as input. In this example, the behavior of the referencevector does not change if the reference has been filtered or notfiltered. If r and s are equal (e.g., some unfiltered reference rhappens to be the same as another filtered reference s) then predictivefunctions, e.g. p_(r)[x,y] (also written as p(x,y,r)) is equal top_(s)[x, y] (also written as p(x,y,s))), applied to filtered andunfiltered references are equal. Additionally, pixel predictions p and qmay be equivalent (e.g., produce the same output given the same input).In such an example, formulas (1)-(8) may be rewritten with pixelprediction p[x,y] replacing pixel prediction q[x,y].

In another example, the prediction (e.g., the sets of functions) maychange depending on the information that a reference has been filtered.In this example, different sets of functions can be denoted (e.g.,p_(r)[x,y] and q_(s)[x,y]). In this case, even if r and s are equal,p_(r)[x,y] and q_(s)[x,y] may not be equal. In other words, the sameinput can create different output depending on whether the input hasbeen filtered or not. In such an example, p[x,y] may not be able to bereplaced by q[x,y].

An advantage of the prediction equations shown is that, with theparameterized formulation, sets of optimal parameters can be determined(i.e., those that optimize the prediction accuracy), for different typesof video textures, using techniques such as training. This approach, inturn, may be extended in some examples by computing several sets ofpredictor parameters, for some typical types of textures, and having acompression scheme where the encoder test predictors from each set, andencodes as side information the one that yields best compression.

In some example of the techniques described above, when the PDPC codingmode is enabled, PDPC parameters used for intra prediction weighting andcontrolling, for example, using filtered or unfiltered samples, of PDPCmode are precomputed and stored in a look up table (LUT). In oneexample, video decoder 30 determines the PDPC parameters according tothe block size and intra prediction direction. Previous techniques forPDPC coding mode assumed that intra predicted blocks are always squarein size.

The JVET test model includes the PDPC coding mode. As discussed above,the JVET test model uses QTBT partitioning, which allows for non-squarerectangular blocks. The following section discusses example techniquesfor the extension of PDPC coding for rectangular blocks. However, itshould be understood that the techniques of this disclosure may be usedfor determining prediction mode parameters for any prediction mode thatuses non-square blocks, including prediction modes that apply a weightedaverage to the predictor and reference samples according to sampleposition.

It is suggested to modify the structure of the LUT used for determiningPDPC parameters, or the techniques used for deriving parameters from theLUT, in a way that for horizontal-related parameters, the width of theblock is used to store or access PDPC parameters from the LUT, and forvertical-related parameters, the height of the block is used to store oraccess PDPC parameters from the LUT. For other parameters that do nothave horizontal or vertical relation, a function of the block width andheight can be applied to store or access those parameters from the LUT.

Video decoder 30 may receive a block of video data that has been encodedusing the PDPC mode. In this example, the block of video data may have anon-square, rectangular shape defined by a width and a height. Videodecoder 30 may determine horizontally-related PDPC parameters as afunction of the intra prediction mode and the width of the block. Videodecoder 30 may determine vertically-related PDPC parameters as afunction of the intra prediction mode and the height of the block. Inaddition, video decoder 30 may determine non-directional PDPC parameters(e.g., PDPC parameters that are neither horizontally-related norvertically-related) based on the intra prediction mode and a function ofthe height and width of the block. Example vertically-related parametersare indicated above with a superscript v. Example horizontally-relatedparameters are indicated above with a superscript h. The function, forexample can be, but is not limited to, the max or min of width andheight of the block, or a weighted average of the height and width ofthe block, where the weighting can be dependent on how one dimension islarger than another dimension of the block. For example, the largerdimension (width or height) can have a larger weight than the otherdimension in the weighted average.

Since there are only a certain number of block shapes (width and height)that are allowed, this function can also be represented explicitly forall possible block widths and heights, or sub-combinations. For example,if we have N_(w) and N_(h) possible block widths and heights, tables ofsize N_(w)×N_(h) can store the data to be used in the intra predictionprocess, for each rectangular or square block.

FIG. 6 is a conceptual diagram illustrating the use of nested tables fordetermining a set of prediction parameters used in a rectangular blockin accordance with one example of the disclosure. Video decoder 30 maydetermine the PDPC parameters using one or more LUTs whose entries areindexed on both the width and height of a block. As shown in FIG. 6, thewidth (W) and/or height (H) may be used as inputs to size-to-parametertable 90. Size-to-parameter table 90 may be configured as a (LUT) thatcontains indices that point to entries in prediction parameter table 92.As discussed above, size-to-parameter table 90 may be of sizeN_(w)×N_(h) to account for N_(w) and N_(h) possible block widths andheights. In this example, size-to-parameter table 90 may be used for asingle intra prediction mode (e.g., DC, planar, or other predictiondirections). In other examples, size-to-parameter table 90 may containentries for all intra prediction modes and use block height, blockwidth, and intra prediction mode as entries in to the table. In general,to minimize memory, video decoder 30 and video encoder 22 may beconfigured to combine table entries in rows and columns, reducing thesize of the tables (e.g., size-to-parameter table 90), and possiblycreating several tables, of different sizes.

As one example, assuming a particular intra prediction mode, videodecoder 30 may use the width of the block of video data being decoded toaccess an entry in size-to-parameter table 90 to determine one or morehorizontally-related PDPC parameters. Based on the width of the block,the corresponding entry in size-to-parameter table 90 may be used as aninput to prediction parameter table 92. Prediction parameter table 92 isof size N_(p)×N_(e) and contains entries of the actual PDPC parameters.As such, the entry obtained from size-to-parameter table 90 is an indexthat points to the actual horizontally-related PDPC parameter inprediction parameter table 92 that is then used in decoding block 94.

Likewise, video decoder 30 may use the height of the block of video databeing decoded to access an entry in size-to-parameter table 90 todetermine one or more vertically-related PDPC parameters. Based on thewidth of the block, the corresponding entry in size-to-parameter table90 may be used as an input to prediction parameter table 92 to obtainthe actual vertically-related PDPC parameter in prediction parametertable 92 that is then used in decoding block 94. The same process may beapplied for non-directional PDPC parameters that are index based on afunction of the height and width of the block.

FIG. 7 is a block diagram illustrating an example video encoder 22 thatmay implement the techniques of this disclosure. FIG. 7 is provided forpurposes of explanation and should not be considered limiting of thetechniques as broadly exemplified and described in this disclosure. Thetechniques of this disclosure may be applicable to various codingstandards or methods.

In the example of FIG. 7, video encoder 22 includes a predictionprocessing unit 100, video data memory 101, a residual generation unit102, a transform processing unit 104, a quantization unit 106, aninverse quantization unit 108, an inverse transform processing unit 110,a reconstruction unit 112, a filter unit 114, a decoded picture buffer116, and an entropy encoding unit 118. Prediction processing unit 100includes an inter prediction processing unit 120 and an intra predictionprocessing unit 126. Inter prediction processing unit 120 may include amotion estimation unit and a motion compensation unit (not shown).

Video data memory 101 may be configured to store video data to beencoded by the components of video encoder 22. The video data stored invideo data memory 101 may be obtained, for example, from video source18. Decoded picture buffer 116 may be a reference picture memory thatstores reference video data for use in encoding video data by videoencoder 22, e.g., in intra- or inter-coding modes. Video data memory 101and decoded picture buffer 116 may be formed by any of a variety ofmemory devices, such as dynamic random access memory (DRAM), includingsynchronous DRAM (SDRAM), magnetoresistive RAM (MRAM), resistive RAM(RRAM), or other types of memory devices. Video data memory 101 anddecoded picture buffer 116 may be provided by the same memory device orseparate memory devices. In various examples, video data memory 101 maybe on-chip with other components of video encoder 22, or off-chiprelative to those components. Video data memory 101 may be the same asor part of storage media 20 of FIG. 1.

Video encoder 22 receives video data. Video encoder 22 may encode eachCTU in a slice of a picture of the video data. Each of the CTUs may beassociated with equally-sized luma coding tree blocks (CTBs) andcorresponding CTBs of the picture. As part of encoding a CTU, predictionprocessing unit 100 may perform partitioning to divide the CTBs of theCTU into progressively-smaller blocks. In some examples, video encoder22 may partition blocks using a QTBT structure. The smaller blocks maybe coding blocks of CUs. For example, prediction processing unit 100 maypartition a CTB associated with a CTU according to a tree structure. Inaccordance with one or more techniques of this disclosure, for eachrespective non-leaf node of the tree structure at each depth level ofthe tree structure, there are a plurality of allowed splitting patternsfor the respective non-leaf node and the video block corresponding tothe respective non-leaf node is partitioned into video blockscorresponding to the child nodes of the respective non-leaf nodeaccording to one of the plurality of allowable splitting patterns.

Video encoder 22 may encode CUs of a CTU to generate encodedrepresentations of the CUs (i.e., coded CUs). As part of encoding a CU,prediction processing unit 100 may partition the coding blocksassociated with the CU among one or more PUs of the CU. Thus, each PUmay be associated with a luma prediction block and corresponding chromaprediction blocks. Video encoder 22 and video decoder 30 may support PUshaving various sizes. As indicated above, the size of a CU may refer tothe size of the luma coding block of the CU and the size of a PU mayrefer to the size of a luma prediction block of the PU. Assuming thatthe size of a particular CU is 2N×2N, video encoder 22 and video decoder30 may support PU sizes of 2N×2N or N×N for intra prediction, andsymmetric PU sizes of 2N×2N, 2N×N, N×2N, N×N, or similar for interprediction. Video encoder 22 and video decoder 30 may also supportasymmetric partitioning for PU sizes of 2N×nU, 2N×nD, nL×2N, and nR×2Nfor inter prediction.

Inter prediction processing unit 120 may generate predictive data for aPU by performing inter prediction on each PU of a CU. The predictivedata for the PU may include predictive blocks of the PU and motioninformation for the PU. Inter prediction processing unit 120 may performdifferent operations for a PU of a CU depending on whether the PU is inan I slice, a P slice, or a B slice. In an I slice, all PUs are intrapredicted. Hence, if the PU is in an I slice, inter predictionprocessing unit 120 does not perform inter prediction on the PU. Thus,for blocks encoded in I-mode, the predicted block is formed usingspatial prediction from previously-encoded neighboring blocks within thesame frame. If a PU is in a P slice, inter prediction processing unit120 may use uni-directional inter prediction to generate a predictiveblock of the PU. If a PU is in a B slice, inter prediction processingunit 120 may use uni-directional or bi-directional inter prediction togenerate a predictive block of the PU.

Intra prediction processing unit 126 may generate predictive data for aPU by performing intra prediction on the PU. The predictive data for thePU may include predictive blocks of the PU and various syntax elements.Intra prediction processing unit 126 may perform intra prediction on PUsin I slices, P slices, and B slices.

To perform intra prediction on a PU, intra prediction processing unit126 may use multiple intra prediction modes to generate multiple sets ofpredictive data for the PU. Intra prediction processing unit 126 may usesamples from sample blocks of neighboring PUs to generate a predictiveblock for a PU. The neighboring PUs may be above, above and to theright, above and to the left, or to the left of the PU, assuming aleft-to-right, top-to-bottom encoding order for PUs, CUs, and CTUs.Intra prediction processing unit 126 may use various numbers of intraprediction modes, e.g., 33 directional intra prediction modes. In someexamples, the number of intra prediction modes may depend on the size ofthe region associated with the PU. In addition, as will be described inmore detail below with reference to FIG. 11, intra prediction processingunit 126 may be configured to determine PDPC parameters for encoding ablock of video data as a function of a height and/or width of a block ofvideo data.

Prediction processing unit 100 may select the predictive data for PUs ofa CU from among the predictive data generated by inter predictionprocessing unit 120 for the PUs or the predictive data generated byintra prediction processing unit 126 for the PUs. In some examples,prediction processing unit 100 selects the predictive data for the PUsof the CU based on rate/distortion metrics of the sets of predictivedata. The predictive blocks of the selected predictive data may bereferred to herein as the selected predictive blocks.

Residual generation unit 102 may generate, based on the coding blocks(e.g., luma, Cb and Cr coding blocks) for a CU and the selectedpredictive blocks (e.g., predictive luma, Cb and Cr blocks) for the PUsof the CU, residual blocks (e.g., luma, Cb and Cr residual blocks) forthe CU. For instance, residual generation unit 102 may generate theresidual blocks of the CU such that each sample in the residual blockshas a value equal to a difference between a sample in a coding block ofthe CU and a corresponding sample in a corresponding selected predictiveblock of a PU of the CU.

Transform processing unit 104 may perform quadtree partitioning topartition the residual blocks associated with a CU into transform blocksassociated with TUs of the CU. Thus, a TU may be associated with a lumatransform block and two chroma transform blocks. The sizes and positionsof the luma and chroma transform blocks of TUs of a CU may or may not bebased on the sizes and positions of prediction blocks of the PUs of theCU. A quadtree structure known as a “residual quadtree” (RQT) mayinclude nodes associated with each of the regions. The TUs of a CU maycorrespond to leaf nodes of the RQT.

Transform processing unit 104 may generate transform coefficient blocksfor each TU of a CU by applying one or more transforms to the transformblocks of the TU. Transform processing unit 104 may apply varioustransforms to a transform block associated with a TU. For example,transform processing unit 104 may apply a discrete cosine transform(DCT), a directional transform, or a conceptually similar transform to atransform block. In some examples, transform processing unit 104 doesnot apply transforms to a transform block. In such examples, thetransform block may be treated as a transform coefficient block.

Quantization unit 106 may quantize the transform coefficients in acoefficient block. The quantization process may reduce the bit depthassociated with some or all of the transform coefficients. For example,an n-bit transform coefficient may be rounded down to an m-bit transformcoefficient during quantization, where n is greater than m. Quantizationunit 106 may quantize a coefficient block associated with a TU of a CUbased on a quantization parameter (QP) value associated with the CU.Video encoder 22 may adjust the degree of quantization applied to thecoefficient blocks associated with a CU by adjusting the QP valueassociated with the CU. Quantization may introduce loss of information.Thus, quantized transform coefficients may have lower precision than theoriginal ones.

Inverse quantization unit 108 and inverse transform processing unit 110may apply inverse quantization and inverse transforms to a coefficientblock, respectively, to reconstruct a residual block from thecoefficient block. Reconstruction unit 112 may add the reconstructedresidual block to corresponding samples from one or more predictiveblocks generated by prediction processing unit 100 to produce areconstructed transform block associated with a TU. By reconstructingtransform blocks for each TU of a CU in this way, video encoder 22 mayreconstruct the coding blocks of the CU.

Filter unit 114 may perform one or more deblocking operations to reduceblocking artifacts in the coding blocks associated with a CU. Decodedpicture buffer 116 may store the reconstructed coding blocks afterfilter unit 114 performs the one or more deblocking operations on thereconstructed coding blocks. Inter prediction processing unit 120 mayuse a reference picture that contains the reconstructed coding blocks toperform inter prediction on PUs of other pictures. In addition, intraprediction processing unit 126 may use reconstructed coding blocks indecoded picture buffer 116 to perform intra prediction on other PUs inthe same picture as the CU.

Entropy encoding unit 118 may receive data from other functionalcomponents of video encoder 22. For example, entropy encoding unit 118may receive coefficient blocks from quantization unit 106 and mayreceive syntax elements from prediction processing unit 100. Entropyencoding unit 118 may perform one or more entropy encoding operations onthe data to generate entropy-encoded data. For example, entropy encodingunit 118 may perform a CABAC operation, a context-adaptive variablelength coding (CAVLC) operation, a variable-to-variable (V2V) lengthcoding operation, a syntax-based context-adaptive binary arithmeticcoding (SBAC) operation, a Probability Interval Partitioning Entropy(PIPE) coding operation, an Exponential-Golomb encoding operation, oranother type of entropy encoding operation on the data. Video encoder 22may output a bitstream that includes entropy-encoded data generated byentropy encoding unit 118. For instance, the bitstream may include datathat represents a RQT for a CU.

FIG. 8 is a block diagram illustrating an example video decoder 30 thatis configured to implement the techniques of this disclosure. FIG. 8 isprovided for purposes of explanation and is not limiting on thetechniques as broadly exemplified and described in this disclosure. Forpurposes of explanation, this disclosure describes video decoder 30 inthe context of HEVC coding. However, the techniques of this disclosuremay be applicable to other coding standards or methods, includingtechniques that allow for non-square partitioning and/or independentluma and chroma partitioning.

In the example of FIG. 8, video decoder 30 includes an entropy decodingunit 150, video data memory 151, a prediction processing unit 152, aninverse quantization unit 154, an inverse transform processing unit 156,a reconstruction unit 158, a filter unit 160, and a decoded picturebuffer 162. Prediction processing unit 152 includes a motioncompensation unit 164 and an intra prediction processing unit 166. Inother examples, video decoder 30 may include more, fewer, or differentfunctional components.

Video data memory 151 may store encoded video data, such as an encodedvideo bitstream, to be decoded by the components of video decoder 30.The video data stored in video data memory 151 may be obtained, forexample, from computer-readable medium 16, e.g., from a local videosource, such as a camera, via wired or wireless network communication ofvideo data, or by accessing physical data storage media. Video datamemory 151 may form a coded picture buffer (CPB) that stores encodedvideo data from an encoded video bitstream. Decoded picture buffer 162may be a reference picture memory that stores reference video data foruse in decoding video data by video decoder 30, e.g., in intra- orinter-coding modes, or for output. Video data memory 151 and decodedpicture buffer 162 may be formed by any of a variety of memory devices,such as dynamic random access memory (DRAM), including synchronous DRAM(SDRAM), magnetoresistive RAM (MRAM), resistive RAM (RRAM), or othertypes of memory devices. Video data memory 151 and decoded picturebuffer 162 may be provided by the same memory device or separate memorydevices. In various examples, video data memory 151 may be on-chip withother components of video decoder 30, or off-chip relative to thosecomponents. Video data memory 151 may be the same as or part of storagemedia 28 of FIG. 1.

Video data memory 151 receives and stores encoded video data (e.g., NALunits) of a bitstream. Entropy decoding unit 150 may receive encodedvideo data (e.g., NAL units) from video data memory 151 and may parsethe NAL units to obtain syntax elements. Entropy decoding unit 150 mayentropy decode entropy-encoded syntax elements in the NAL units.Prediction processing unit 152, inverse quantization unit 154, inversetransform processing unit 156, reconstruction unit 158, and filter unit160 may generate decoded video data based on the syntax elementsextracted from the bitstream. Entropy decoding unit 150 may perform aprocess generally reciprocal to that of entropy encoding unit 118.

In accordance with some examples of this disclosure, entropy decodingunit 150 may determine a tree structure as part of obtaining the syntaxelements from the bitstream. The tree structure may specify how aninitial video block, such as a CTB, is partitioned into smaller videoblocks, such as coding units. In accordance with one or more techniquesof this disclosure, for each respective non-leaf node of the treestructure at each depth level of the tree structure, there are aplurality of allowed splitting patterns for the respective non-leaf nodeand the video block corresponding to the respective non-leaf node ispartitioned into video blocks corresponding to the child nodes of therespective non-leaf node according to one of the plurality of allowablesplitting patterns.

In addition, as will be explained in more detail below with reference toFIG. 10, video decoder 30 may be configured to determine how to reusecoding mode information received for a luma block for use when decodingchroma blocks in situations where there are two or more luma blocks thatcorrespond to a single chroma block.

In addition to obtaining syntax elements from the bitstream, videodecoder 30 may perform a reconstruction operation on a non-partitionedCU. To perform the reconstruction operation on a CU, video decoder 30may perform a reconstruction operation on each TU of the CU. Byperforming the reconstruction operation for each TU of the CU, videodecoder 30 may reconstruct residual blocks of the CU.

As part of performing a reconstruction operation on a TU of a CU,inverse quantization unit 154 may inverse quantize, i.e., de-quantize,coefficient blocks associated with the TU. After inverse quantizationunit 154 inverse quantizes a coefficient block, inverse transformprocessing unit 156 may apply one or more inverse transforms to thecoefficient block in order to generate a residual block associated withthe TU. For example, inverse transform processing unit 156 may apply aninverse DCT, an inverse integer transform, an inverse Karhunen-Loevetransform (KLT), an inverse rotational transform, an inverse directionaltransform, or another inverse transform to the coefficient block.

If a PU is encoded using intra prediction, intra prediction processingunit 166 may perform intra prediction to generate predictive blocks ofthe PU. Intra prediction processing unit 166 may use an intra predictionmode to generate the predictive blocks of the PU based on samplesspatially-neighboring blocks. Intra prediction processing unit 166 maydetermine the intra prediction mode for the PU based on one or moresyntax elements obtained from the bitstream. In addition, as will bedescribed in more detail below with reference to FIG. 12, intraprediction processing unit 166 may be configured to determine PDPCparameters for encoding a block of video data as a function of a heightand/or width of a block of video data.

If a PU is encoded using inter prediction, entropy decoding unit 150 maydetermine motion information for the PU. Motion compensation unit 164may determine, based on the motion information of the PU, one or morereference blocks. Motion compensation unit 164 may generate, based onthe one or more reference blocks, predictive blocks (e.g., predictiveluma, Cb and Cr blocks) for the PU.

Reconstruction unit 158 may use transform blocks (e.g., luma, Cb and Crtransform blocks) for TUs of a CU and the predictive blocks (e.g., luma,Cb and Cr blocks) of the PUs of the CU, i.e., either intra predictiondata or inter prediction data, as applicable, to reconstruct the codingblocks (e.g., luma, Cb and Cr coding blocks) for the CU. For example,reconstruction unit 158 may add samples of the transform blocks (e.g.,luma, Cb and Cr transform blocks) to corresponding samples of thepredictive blocks (e.g., luma, Cb and Cr predictive blocks) toreconstruct the coding blocks (e.g., luma, Cb and Cr coding blocks) ofthe CU.

Filter unit 160 may perform a deblocking operation to reduce blockingartifacts associated with the coding blocks of the CU. Video decoder 30may store the coding blocks of the CU in decoded picture buffer 162.Decoded picture buffer 162 may provide reference pictures for subsequentmotion compensation, intra prediction, and presentation on a displaydevice, such as display device 32 of FIG. 1. For instance, video decoder30 may perform, based on the blocks in decoded picture buffer 162, intraprediction or inter prediction operations for PUs of other CUs.

FIG. 9 is a flowchart illustrating an example operation of a video coderin accordance with a technique of this disclosure. The video coder maybe video encoder 22 and/or video decoder 30. In accordance with thetechniques of this disclosure, encoder 22 and/or video decoder 30 may beconfigured to partition video data into partitions of luma components(200), partition the video data into partitions of chroma components,wherein the chroma components are partitioned independently of the lumacomponents (202), code a first partition of the luma components (204),code a syntax element indicating if information associated with codingthe first partition of the luma components is to be used for coding asecond partition of the chroma components (206), and code the secondpartition of the chroma components in accordance with the syntax element(208).

FIG. 10 is a flowchart illustrating an example operation of a videodecoder in accordance with a technique of this disclosure. Thetechniques of FIG. 10 may be performed by one or more hardwarestructures of video decoder 30.

In one example of the disclosure, video decoder 30 may be configured toreceive the bitstream of encoded video data, the encoded video datarepresenting partitioned luma blocks and partitioned chroma blocks,wherein the chroma blocks are partitioned independently of the lumablocks (212). Video decoder 30 may be further configured to determine arespective coding mode corresponding to the respective partitioned lumablocks (214), and decode the respective partitioned luma blocksaccording the determined respective coding modes (216).

Video decoder 30 may be further configured to decode a first syntaxelement indicating that the respective coding modes associated with therespective partitioned luma blocks are to be used for decoding a firstpartitioned chroma block, wherein the first partitioned chroma block isaligned with two or more partitioned luma blocks (218). Video decoder 30may further determine a chroma coding mode for the first partitionedchroma block according to a function of the respective coding modes ofthe two or more partitioned luma blocks (220), and decode the firstpartitioned chroma block in accordance with the determined chroma codingmode (222).

In one example of the disclosure, the chroma blocks are partitionedindependently of the luma blocks such that at least one partitionedchroma block is not aligned with a single partitioned luma block.

In another example of the disclosure, to determine the respective codingmode corresponding to the respective partitioned luma blocks, videodecoder 30 may be further configured to receive second syntax elementscorresponding to the respective partitioned luma blocks, the secondsyntax elements indicating the respective coding mode, and decode thesecond syntax elements corresponding to the respective partitioned lumablocks to determine the respective coding mode.

In another example of the disclosure, to determine the respective codingmode corresponding to the respective partitioned luma blocks, videodecoder 30 is further configured to select one or more respective codingmodes from one or more representative locations of the respectivepartitioned luma blocks. In another example, video decoder 30 isconfigured to select the one or more respective coding modes accordingto the function.

In another example, the one or more representative locations include acenter representative location of the respective partitioned lumablocks, and wherein to determine the chroma coding mode for the firstpartitioned chroma block according to the function, video decoder 30 isfurther configured to obtain information indicating the determinedrespective coding mode stored for the center representative location.

In another example, the one or more representative locations include acorner representative location of the respective partitioned lumablocks, and wherein to determine the chroma coding mode for the firstpartitioned chroma block according to the function, video decoder 30 isfurther configured to obtain information indicating the determinedrespective coding mode stored for the corner representative location. Inone example, the one or more representative locations comprise one ormore sub-blocks.

In another example of the disclosure, video decoder 30 may be furtherconfigured to divide the respective partitioned luma blocks intorespective sub-blocks, and store information indicating the determinedrespective coding mode in respective memory locations associated withthe respective sub-blocks.

In another example of the disclosure, the function includes a locationof one or more respective sub-blocks of the two or more partitioned lumablocks. In another example of the disclosure, the location of the one ormore respective sub-blocks is a center sub-block of the two or morepartitioned luma blocks, and wherein to determine the chroma coding modefor the first partitioned chroma block according to the function, videodecoder 30 is configured to obtain the information indicating thedetermined respective coding mode stored for the center sub-block.

In another example of the disclosure, the location of the one or morerespective sub-blocks is a corner sub-block of the two more partitionedluma blocks, and wherein to determine the chroma coding mode for thefirst partitioned chroma block according to the function, the videodecoder 30 is configured to obtain the information indicating thedetermined respective coding mode stored for the corner sub-block.

In another example of the disclosure, the function includes astatistical analysis of the information indicating the determinedrespective coding mode in respective memory locations associated withthe respective sub-blocks.

In another example of the disclosure, to determine the chroma codingmode for the first partitioned chroma block according to the function,video decoder 30 is further configured to analyze the information storedin the respective memory locations using one of a gradient or a higherderivative.

In another example of the disclosure, the information includes one ormore of an indication of a direct mode for chroma prediction, aprediction direction, motion information, a flag for a positiondependent intra prediction combination mode, one or more parameters forthe position dependent intra prediction combination mode, one or moresecond transform sets for a non-separable transform, an enhancedmultiple transform, an adaptive multiple transform, or one or morecontexts for determining entropy coding data models.

In another example of the disclosure, video decoder 30 may configured toreceive a third syntax element indicating the function.

In another example of the disclosure, video decoder 30 is part of awireless communication device, the wireless communication device furthercomprising a receiver configured to receive the bitstream of encodedvideo data. In one example, the wireless communication device is amobile station and the bitstream of encoded video data is received bythe receiver and modulated according to a cellular communicationstandard.

FIG. 11 is a flowchart illustrating an example operation of videoencoder 22 in accordance with a technique of this disclosure. Thetechniques of FIG. 12 may be performed by one or more hardwarestructures of video encoder 22.

In one example of the disclosure, video encoder 22 may be configured toreceive a block of video data, the block of video data having anon-square shape defined by a width and a height (230), determine one ormore PDPC parameters based on one or more of the width or the height ofthe block of video data (232), and encode the block of video data usinga PDPC mode and the determined PDPC parameters (234). As discussedabove, it should be understood that the techniques FIG. 11 may be usedfor determining prediction mode parameters for any prediction mode thatuses non-square blocks, including prediction modes that apply a weightedaverage to the predictor and reference samples according to sampleposition.

In one example, the one or more PDPC parameters include one or morehorizontally-related PDPC parameters and one or more vertically-relatedPDPC parameters, and wherein to determine the one or more PDPCparameters, video encoder 22 is further configured to determine the oneor more horizontally-related PDPC parameters based on the width of theblock of video data, and determine the one or more vertically-relatedPDPC parameters based on the height of the block of video data.

In another example of the disclosure, to determine the one or morehorizontally-related PDPC parameters, video encoder 22 is furtherconfigured to retrieve one or more entries of one or more lookup tablesas a function of the width of the block of video data, and wherein todetermine the one or more vertically-related PDPC parameters, videoencoder 22 is further configured to retrieve one or more entries of theone or more lookup tables as a function of the height of the block ofvideo data.

In another example of the disclosure, to retrieve the one or moreentries of the one or more lookup tables as the function of the width ofthe block of video data, video encoder 22 is further configured toretrieve a first index in a first lookup table based on the width of theblock of video data, the first index pointing to a first entry in asecond lookup table, and retrieve the one or more horizontally-relatedPDPC parameters in the second lookup table based on the retrieved firstindex. In a further example, to retrieve the one or more entries of theone or more lookup tables as the function of the of the height of theblock of video data, video encoder 22 is further configured to retrievea second index in the first lookup table based on the height of theblock of video data, the second index pointing to a second entry in thesecond lookup table, and retrieve the one or more vertically-relatedPDPC parameters in the second lookup table based on the retrieved secondindex.

In another example of the disclosure, the one or more PDPC parametersinclude one or more non-directional PDPC parameters that are nothorizontally-related and are not vertically-related, and wherein todetermine the one or more PDPC parameters, video encoder 22 is furtherconfigured to determine the one or more non-directional PDPC parametersbased on a function of the width and the height of the block of videodata.

In another example of the disclosure, the function is one or more of aminimum of the width and the height of the block of video data, amaximum of the width and the height of the block of video data, or aweighted average of the width and the height of the block of video data.In a further example, to determine the one or more non-directional PDPCparameters, video encoder 22 is further configured to access one or moreentries of one or more lookup tables as a function of the width and theheight of the block of video data.

In another example of the disclosure, video encoder 22 is included in awireless communication device, the wireless communication device furthercomprising a transmitter configured to transmit the encoded block ofvideo data. In another example, the wireless communication device is amobile station and the encoded block of video data is transmitted by thetransmitter and modulated according to a cellular communicationstandard.

FIG. 12 is a flowchart illustrating an example operation of videodecoder 30 in accordance with a technique of this disclosure. Thetechniques of FIG. 12 may be performed by one or more hardwarestructures of video decoder 30.

In one example of the disclosure, video decoder 30 is configured toreceive a block of video data encoded using a PDPC mode, the block ofvideo data having a non-square shape defined by a width and a height(240), determine one or more PDPC parameters based on one or more of thewidth or the height of the block of video data (242), and decode theblock of video data using the PDPC mode and the determined PDPCparameters (244). As discussed above, it should be understood that thetechniques FIG. 12 may be used for determining prediction modeparameters for any prediction mode that uses non-square blocks,including prediction modes that apply a weighted average to thepredictor and reference samples according to sample position.

In one example of the disclosure, the one or more PDPC parametersinclude one or more horizontally-related PDPC parameters and one or morevertically-related PDPC parameters, and wherein to determine the one ormore PDPC parameters, video decoder 30 is further configured todetermine the one or more horizontally-related PDPC parameters based onthe width of the block of video data, and determine the one or morevertically-related PDPC parameters based on the height of the block ofvideo data.

In another example of the disclosure, to determine the one or morehorizontally-related PDPC parameters, video decoder 30 is furtherconfigured to retrieve one or more entries of one or more lookup tablesas a function of the width of the block of video data, and wherein todetermine the one or more vertically-related PDPC parameters, videodecoder 30 is further configured to retrieve one or more entries of theone or more lookup tables as a function of the height of the block ofvideo data.

In another example of the disclosure, to retrieve the one or moreentries of the one or more lookup tables as the function of the width ofthe block of video data, video decoder 30 is further configured toretrieve a first index in a first lookup table based on the width of theblock of video data, the first index pointing to a first entry in asecond lookup table, and retrieve the one or more horizontally-relatedPDPC parameters in the second lookup table based on the retrieved firstindex. In a further example, to retrieve the one or more entries of theone or more lookup tables as the function of the of the height of theblock of video data, video decoder 30 is further configured to retrievea second index in the first lookup table based on the height of theblock of video data, the second index pointing to a second entry in thesecond lookup table, and retrieve the one or more vertically-relatedPDPC parameters in the second lookup table based on the retrieved secondindex.

In another example, the one or more PDPC parameters include one or morenon-directional PDPC parameters that are not horizontally-related andare not vertically-related, and wherein to determine the one or morePDPC parameters, video decoder 30 is further configured to determine theone or more non-directional PDPC parameters based on a function of thewidth and the height of the block of video data.

In another example, the function is one or more of a minimum of thewidth and the height of the block of video data, a maximum of the widthand the height of the block of video data, or a weighted average of thewidth and the height of the block of video data.

In another example of the disclosure, to determine the one or morenon-directional PDPC parameters, video decoder 30 is further configuredto access one or more entries of one or more lookup tables as a functionof the width and the height of the block of video data.

In another example of the disclosure, video decoder 30 is part of is awireless communication device, the wireless communication device furthercomprising a receiver configured to receive the block of video data. Ina further example, the wireless communication device is a mobile stationand the block of video data is received by the receiver and modulatedaccording to a cellular communication standard.

Certain aspects of this disclosure have been described with respect toextensions of the HEVC standard for purposes of illustration. However,the techniques described in this disclosure may be useful for othervideo coding processes, including other standard or proprietary videocoding processes under development or not yet developed.

A video coder, as described in this disclosure, may refer to a videoencoder or a video decoder. Similarly, a video coding unit may refer toa video encoder or a video decoder. Likewise, video coding may refer tovideo encoding or video decoding, as applicable.

It is to be recognized that depending on the example, certain acts orevents of any of the techniques described herein can be performed in adifferent sequence, may be added, merged, or left out altogether (e.g.,not all described acts or events are necessary for the practice of thetechniques). Moreover, in certain examples, acts or events may beperformed concurrently, e.g., through multi-threaded processing,interrupt processing, or multiple processors, rather than sequentially.

In one or more examples, the functions described may be implemented inhardware, software, firmware, or any combination thereof. If implementedin software, the functions may be stored on or transmitted over as oneor more instructions or code on a computer-readable medium and executedby a hardware-based processing unit. Computer-readable media may includecomputer-readable storage media, which corresponds to a tangible mediumsuch as data storage media, or communication media including any mediumthat facilitates transfer of a computer program from one place toanother, e.g., according to a communication protocol. In this manner,computer-readable media generally may correspond to (1) tangiblecomputer-readable storage media which is non-transitory or (2) acommunication medium such as a signal or carrier wave. Data storagemedia may be any available media that can be accessed by one or morecomputers or one or more processors to retrieve instructions, codeand/or data structures for implementation of the techniques described inthis disclosure. A computer program product may include acomputer-readable medium.

By way of example, and not limitation, such computer-readable storagemedia can comprise RAM, ROM, EEPROM, CD-ROM or other optical diskstorage, magnetic disk storage, or other magnetic storage devices, flashmemory, or any other medium that can be used to store desired programcode in the form of instructions or data structures and that can beaccessed by a computer. Also, any connection is properly termed acomputer-readable medium. For example, if instructions are transmittedfrom a website, server, or other remote source using a coaxial cable,fiber optic cable, twisted pair, digital subscriber line (DSL), orwireless technologies such as infrared, radio, and microwave, then thecoaxial cable, fiber optic cable, twisted pair, DSL, or wirelesstechnologies such as infrared, radio, and microwave are included in thedefinition of medium. It should be understood, however, thatcomputer-readable storage media and data storage media do not includeconnections, carrier waves, signals, or other transitory media, but areinstead directed to non-transitory, tangible storage media. Disk anddisc, as used herein, includes compact disc (CD), laser disc, opticaldisc, digital versatile disc (DVD), floppy disk and Blu-ray disc, wheredisks usually reproduce data magnetically, while discs reproduce dataoptically with lasers. Combinations of the above should also be includedwithin the scope of computer-readable media.

Instructions may be executed by one or more processors, such as one ormore digital signal processors (DSPs), general purpose microprocessors,application specific integrated circuits (ASICs), field programmablelogic arrays (FPGAs), or other equivalent integrated or discrete logiccircuitry. Accordingly, the term “processor,” as used herein may referto any of the foregoing structure or any other structure suitable forimplementation of the techniques described herein. In addition, in someaspects, the functionality described herein may be provided withindedicated hardware and/or software modules configured for encoding anddecoding, or incorporated in a combined codec. Also, the techniquescould be fully implemented in one or more circuits or logic elements.

The techniques of this disclosure may be implemented in a wide varietyof devices or apparatuses, including a wireless handset, an integratedcircuit (IC) or a set of ICs (e.g., a chip set). Various components,modules, or units are described in this disclosure to emphasizefunctional aspects of devices configured to perform the disclosedtechniques, but do not necessarily require realization by differenthardware units. Rather, as described above, various units may becombined in a codec hardware unit or provided by a collection ofinteroperative hardware units, including one or more processors asdescribed above, in conjunction with suitable software and/or firmware.

Various examples have been described. These and other examples arewithin the scope of the following claims.

What is claimed is:
 1. A method of decoding video data, the methodcomprising: receiving a bitstream of encoded video data, the encodedvideo data representing partitioned luma blocks and partitioned chromablocks, wherein the chroma blocks are partitioned independently of theluma blocks; determining a respective coding mode corresponding to therespective partitioned luma blocks, wherein the respective coding modeincludes one or more of a direct mode, a position dependent intraprediction combination mode, one or more second transform sets for anon-separable transform mode, an enhanced multiple transform mode, or anadaptive multiple transform mode; decoding the respective partitionedluma blocks according to the determined respective coding modes;decoding a first syntax element indicating that the respective codingmodes associated with the respective partitioned luma blocks are to beused for decoding a first partitioned chroma block, wherein the firstpartitioned chroma block is aligned with two or more partitioned lumablocks; determining a chroma coding mode for the first partitionedchroma block according to a function of the respective coding mode of aluma sub-block of the two or more partitioned luma blocks; and decodingthe first partitioned chroma block in accordance with the determinedchroma coding mode.
 2. The method of claim 1, wherein the chroma blocksare partitioned independently of the luma blocks such that at least onepartitioned chroma block is not aligned with a single partitioned lumablock.
 3. The method of claim 1, wherein determining the respectivecoding mode corresponding to the respective partitioned luma blockscomprises: receiving second syntax elements corresponding to therespective partitioned luma blocks, the second syntax elementsindicating the respective coding mode; and decoding the second syntaxelements corresponding to the respective partitioned luma blocks todetermine the respective coding mode.
 4. The method of claim 1, whereindetermining the respective coding mode corresponding to the respectivepartitioned luma blocks comprises: selecting one or more respectivecoding modes from one or more representative locations of the respectivepartitioned luma blocks.
 5. The method of claim 4, wherein selecting theone or more respective coding modes comprises selecting the one or morerespective coding modes according to the function.
 6. The method ofclaim 4, wherein the one or more representative locations include acenter representative location of the respective partitioned lumablocks, and wherein determining the chroma coding mode for the firstpartitioned chroma block according to the function comprises: obtaininginformation indicating the determined respective coding mode stored forthe center representative location.
 7. The method of claim 4, whereinthe one or more representative locations include a corner representativelocation of the respective partitioned luma blocks, and whereindetermining the chroma coding mode for the first partitioned chromablock according to the function comprises: obtaining informationindicating the determined respective coding mode stored for the cornerrepresentative location.
 8. The method of claim 4, wherein the one ormore representative locations comprise one or more sub-blocks.
 9. Themethod of claim 1, further comprising: dividing the respectivepartitioned luma blocks into respective sub-blocks; and storinginformation indicating the determined respective coding mode inrespective memory locations associated with the respective sub-blocks.10. The method of claim 9, wherein the function includes a statisticalanalysis of the information indicating the determined respective codingmode in respective memory locations associated with the respectivesub-blocks.
 11. The method of claim 10, wherein determining the chromacoding mode for the first partitioned chroma block according to thefunction comprises: analyzing the information stored in the respectivememory locations using one of a gradient or a higher derivative.
 12. Themethod of claim 11, wherein the information includes one or more of anindication of a direct mode for chroma prediction, a predictiondirection, motion information, a flag for a position dependent intraprediction combination mode, one or more parameters for the positiondependent intra prediction combination mode, one or more secondtransform sets for a non-separable transform, an enhanced multipletransform, an adaptive multiple transform, or one or more contexts fordetermining entropy coding data models.
 13. The method of claim 1,further comprising: receiving a third syntax element indicating thefunction.
 14. The method of claim 1, the method being executable on awireless communication device, wherein the device comprises: a memoryconfigured to store the encoded video data; a processor configured toexecute instructions to process the encoded video data stored in thememory; and a receiver configured to receive the bitstream of encodedvideo data.
 15. The method of claim 14, wherein the wirelesscommunication device is a mobile station and the bitstream of encodedvideo data is received by the receiver and modulated according to acellular communication standard.
 16. An apparatus configured to decodevideo data, the apparatus comprising: a memory configured to store abitstream of encoded video data; and one or more processors configuredto: receive the bitstream of encoded video data, the encoded video datarepresenting partitioned luma blocks and partitioned chroma blocks,wherein the chroma blocks are partitioned independently of the lumablocks; determine a respective coding mode corresponding to therespective partitioned luma blocks, wherein the respective coding modeincludes one or more of a direct mode, a position dependent intraprediction combination mode, one or more second transform sets for anon-separable transform mode, an enhanced multiple transform mode, or anadaptive multiple transform mode; decode the respective partitioned lumablocks according to the determined respective coding modes; decode afirst syntax element indicating that the respective coding modesassociated with the respective partitioned luma blocks are to be usedfor decoding a first partitioned chroma block, wherein the firstpartitioned chroma block is aligned with two or more partitioned lumablocks; determine a chroma coding mode for the first partitioned chromablock according to a function of the respective coding mode of a lumasub-block of the two or more partitioned luma blocks; and decode thefirst partitioned chroma block in accordance with the determined chromacoding mode.
 17. The apparatus of claim 16, wherein the chroma blocksare partitioned independently of the luma blocks such that at least onepartitioned chroma block is not aligned with a single partitioned lumablock.
 18. The apparatus of claim 16, wherein to determine therespective coding mode corresponding to the respective partitioned lumablocks, the one or more processors are further configured to: receivesecond syntax elements corresponding to the respective partitioned lumablocks, the second syntax elements indicating the respective codingmode; and decode the second syntax elements corresponding to therespective partitioned luma blocks to determine the respective codingmode.
 19. The apparatus of claim 16, wherein to determine the respectivecoding mode corresponding to the respective partitioned luma blocks, theone or more processors are further configured to: select one or morerespective coding modes from one or more representative locations of therespective partitioned luma blocks.
 20. The apparatus of claim 19,wherein to select the one or more respective coding modes, the one ormore processors are further configured to select the one or morerespective coding modes according to the function.
 21. The apparatus ofclaim 19, wherein the one or more representative locations include acenter representative location of the respective partitioned lumablocks, and wherein to determine the chroma coding mode for the firstpartitioned chroma block according to the function, the one or moreprocessors are further configured to: obtain information indicating thedetermined respective coding mode stored for the center representativelocation.
 22. The apparatus of claim 19, wherein the one or morerepresentative locations include a corner representative location of therespective partitioned luma blocks, and wherein to determine the chromacoding mode for the first partitioned chroma block according to thefunction, the one or more processors are further configured to: obtaininformation indicating the determined respective coding mode stored forthe corner representative location.
 23. The apparatus of claim 19,wherein the one or more representative locations comprise one or moresub-blocks.
 24. The apparatus of claim 16, wherein the one or moreprocessors are further configured to: divide the respective partitionedluma blocks into respective sub-blocks; and store information indicatingthe determined respective coding mode in respective memory locationsassociated with the respective sub-blocks.
 25. The apparatus of claim24, wherein the function includes a statistical analysis of theinformation indicating the determined respective coding mode inrespective memory locations associated with the respective sub-blocks.26. The apparatus of claim 25, wherein to determine the chroma codingmode for the first partitioned chroma block according to the function,the one or more processors are further configured to: analyze theinformation stored in the respective memory locations using one of agradient or a higher derivative.
 27. The apparatus of claim 26, whereinthe information includes one or more of an indication of a direct modefor chroma prediction, a prediction direction, motion information, aflag for a position dependent intra prediction combination mode, one ormore parameters for the position dependent intra prediction combinationmode, one or more second transform sets for a non-separable transform,an enhanced multiple transform, an adaptive multiple transform, or oneor more contexts for determining entropy coding data models.
 28. Theapparatus of claim 16, wherein the one or more processors are furtherconfigured to: receive a third syntax element indicating the function.29. The apparatus of claim 16, wherein the apparatus is a wirelesscommunication device, the apparatus further comprising: a receiverconfigured to receive the bitstream of encoded video data.
 30. Theapparatus of claim 29, wherein the wireless communication device is amobile station and the bitstream of encoded video data is received bythe receiver and modulated according to a cellular communicationstandard.
 31. An apparatus configured to decode video data, theapparatus comprising: means for receiving a bitstream of encoded videodata, the encoded video data representing partitioned luma blocks andpartitioned chroma blocks, wherein the chroma blocks are partitionedindependently of the luma blocks; means for determining a respectivecoding mode corresponding to the respective partitioned luma blocks,wherein the respective coding mode includes one or more of a directmode, a position dependent intra prediction combination mode, one ormore second transform sets for a non-separable transform mode, anenhanced multiple transform mode, or an adaptive multiple transformmode; means for decoding the respective partitioned luma blocksaccording to the determined respective coding modes; means for decodinga first syntax element indicating that the respective coding modesassociated with the respective partitioned luma blocks are to be usedfor decoding a first partitioned chroma block, wherein the firstpartitioned chroma block is aligned with two or more partitioned lumablocks; means for determining a chroma coding mode for the firstpartitioned chroma block according to a function of the respectivecoding mode of a luma sub-block of the two or more partitioned lumablocks; and means for decoding the first partitioned chroma block inaccordance with the determined chroma coding mode.
 32. The apparatus ofclaim 31, wherein the chroma blocks are partitioned independently of theluma blocks such that at least one partitioned chroma block is notaligned with a single partitioned luma block.
 33. A non-transitorycomputer-readable storage medium having instructions stored thereonthat, when executed, causes one or more processors configured to decodedvideo data to: receive the bitstream of encoded video data, the encodedvideo data representing partitioned luma blocks and partitioned chromablocks, wherein the chroma blocks are partitioned independently of theluma blocks; determine a respective coding mode corresponding to therespective partitioned luma blocks, wherein the respective coding modeincludes one or more of a direct mode, a position dependent intraprediction combination mode, one or more second transform sets for anon-separable transform mode, an enhanced multiple transform mode, or anadaptive multiple transform mode; decode the respective partitioned lumablocks according to the determined respective coding modes; decode afirst syntax element indicating that the respective coding modesassociated with the respective partitioned luma blocks are to be usedfor decoding a first partitioned chroma block, wherein the firstpartitioned chroma block is aligned with two or more partitioned lumablocks; determine a chroma coding mode for the first partitioned chromablock according to a function of the respective coding mode of a lumasub-block of the two or more partitioned luma blocks; and decode thefirst partitioned chroma block in accordance with the determined chromacoding mode.
 34. The non-transitory computer-readable storage medium ofclaim 33, wherein the chroma blocks are partitioned independently of theluma blocks such that at least one partitioned chroma block is notaligned with a single partitioned luma block.
 35. The method of claim 9,wherein the function includes a location of one or more respectivesub-blocks of the two or more partitioned luma blocks.
 36. The method ofclaim 35, wherein the location of the one or more respective sub-blocksis a center sub-block of the two or more partitioned luma blocks, andwherein determining the chroma coding mode for the first partitionedchroma block according to the function comprises: obtaining theinformation indicating the determined respective coding mode stored forthe center sub-block.
 37. The method of claim 35, wherein the locationof the one or more respective sub-blocks is a corner sub-block of thetwo more partitioned luma blocks, and wherein determining the chromacoding mode for the first partitioned chroma block according to thefunction comprises: obtaining the information indicating the determinedrespective coding mode stored for the corner sub-block.
 38. Theapparatus of claim 24, wherein the function includes a location of oneor more respective sub-blocks of the two or more partitioned lumablocks.
 39. The apparatus of claim 38, wherein the location of the oneor more respective sub-blocks is a center sub-block of the two or morepartitioned luma blocks, and wherein to determine the chroma coding modefor the first partitioned chroma block according to the function, theone or more processors are further configured to: obtain the informationindicating the determined respective coding mode stored for the centersub-block.
 40. The apparatus of claim 38, wherein the location of theone or more respective sub-blocks is a corner sub-block of the two morepartitioned luma blocks, and wherein to determine the chroma coding modefor the first partitioned chroma block according to the function, theone or more processors are further configured to: obtain the informationindicating the determined respective coding mode stored for the cornersub-block.